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All questions of Conservation of Energy for Grade 8 Exam
If a light bulb is switched on for 20 s and it consumes 2400 J of electrical energy then it's power is- a)60 W
- b)70 W
- c)80 W
- d)90 W
Correct answer is option 'A'. Can you explain this answer?
If a light bulb is switched on for 20 s and it consumes 2400 J of electrical energy then it's power is
a)
60 W
b)
70 W
c)
80 W
d)
90 W
|
Gayatri bajaj answered |
Power = Energy /Time
Power = 2400/20
Power = 120w
Power = 2400/20
Power = 120w
A diesel engine supplies 25,000 J of energy in 50 seconds. Power of engine would be- a)7500 W
- b)250 W
- c)25000 W
- d)500 W
Correct answer is option 'D'. Can you explain this answer?
A diesel engine supplies 25,000 J of energy in 50 seconds. Power of engine would be
a)
7500 W
b)
250 W
c)
25000 W
d)
500 W
|
Amit Sharma answered |
Power = Work done / Time
= 25000 / 50
= 500J/s or 500W
= 25000 / 50
= 500J/s or 500W
The shape of an aeroplane is like a- a)Bird
- b)Car
- c)Dog
- d)All.
Correct answer is option 'A'. Can you explain this answer?
The shape of an aeroplane is like a
a)
Bird
b)
Car
c)
Dog
d)
All.
|
Vivek Rana answered |
Airplanes have wings, just like birds. They also have a light Skelton to decrease their weight, and they have a streamlined shape to decrease drag. Airplanes wings are designed to create lift by changing the pressure, rather than by flapping them up and down.
Fluids are only liquids.- a)True
- b)False
Correct answer is option 'B'. Can you explain this answer?
Fluids are only liquids.
a)
True
b)
False
|
Kavya Saxena answered |
A fluid is a substance that continually flows under an applied shear stress, or external force. Fluids are a phase of matter and include liquids, gases and plasmas.
Sliding friction is ______________ than static friction.- a)More
- b)Equal
- c)Greater
- d)Less
Correct answer is option 'D'. Can you explain this answer?
Sliding friction is ______________ than static friction.
a)
More
b)
Equal
c)
Greater
d)
Less
|
|
Amit Sharma answered |
- Friction comes into play when irregularities present in the surfaces of two objects in contact get interlocked with each other.
- In sliding, the time given for interlocking is very small. Hence, the interlocking is not strong.
- Therefore, less force is required to overcome this interlocking. Because of this reason, sliding friction is less than static friction.
Rolling friction is smaller than- a)Sliding friction
- b)Static friction
- c)Fluid friction
- d)All of the above.
Correct answer is option 'D'. Can you explain this answer?
Rolling friction is smaller than
a)
Sliding friction
b)
Static friction
c)
Fluid friction
d)
All of the above.
|
Malavika Basu answered |
No the correct answer is
(a) Sliding friction
Explanation: Friction is the force which resists the relative motion between two surfaces in contact.
Now, rolling friction comes into play between two surfaces, when one body rolls over the other and sliding friction comes into play when when one body slides or tends to slide over the surface of another body; it tends to reduce the relative velocity between the two surfaces during sliding. Now, if the area of contact between the two surfaces can somehow be reduced, then the effect of friction between the two surfaces will be drastically reduced.
When an object slides across the ground, it has much more surface area in direct contact with the ground, which means that the amount of friction is significantly higher. When an object rolls along the ground, only a minuscule point on the object contacts the ground at any point in time, making the stopping force much weaker.
Moreover, in sliding motion, the heights of cavities (irregularities) are to climb up which introduces the friction, while rolling friction, the heights of cavitites are to cross over which avoid the friction.
A toy car released with the same initial speed will travel farthest on- a)Muddy surface
- b)Cemented surface
- c)Brick surface
- d)Polished marble surface
Correct answer is option 'D'. Can you explain this answer?
A toy car released with the same initial speed will travel farthest on
a)
Muddy surface
b)
Cemented surface
c)
Brick surface
d)
Polished marble surface
|
|
Kavya Saxena answered |
A polished marble surface has the least frictional force, hence a car will travel farther on a marble floor.
Fluid friction can be minimized by:
- a)Adding salts to fluid
- b)Increasing volume
- c)Giving suitable shape
- d)Decreasing volume
Correct answer is option 'C'. Can you explain this answer?
Fluid friction can be minimized by:
a)
Adding salts to fluid
b)
Increasing volume
c)
Giving suitable shape
d)
Decreasing volume
|
Aniket Choudhary answered |
Fluid friction can be minimized by giving suitable shapes to the objects moving in the fluids.
What is the commercial unit of energy?- a)electron volt
- b)W/s
- c)kW h
- d)joule
Correct answer is option 'C'. Can you explain this answer?
What is the commercial unit of energy?
a)
electron volt
b)
W/s
c)
kW h
d)
joule
|
Rajesh Seervi answered |
C is correct answer because energy consumed in commercial use in per unit time and which is defined as power and power has unit watt . We take kWh because energy consumed in commercial use have high value so kWh is taken.
A stone weighing 1 kg is dropped from rest from a height of 4 metres above the ground. When it has free-fallen 1 metre its total energy with respect to the ground is- a)15 J
- b)40 J
- c)20 J
- d)30 J
Correct answer is option 'B'. Can you explain this answer?
A stone weighing 1 kg is dropped from rest from a height of 4 metres above the ground. When it has free-fallen 1 metre its total energy with respect to the ground is
a)
15 J
b)
40 J
c)
20 J
d)
30 J
|
Gitanjali Mukherjee answered |
**Explanation:**
When an object is dropped from a height, it undergoes free fall. During free fall, the only force acting on the object is the force of gravity. As the object falls, its potential energy is converted into kinetic energy.
**Step 1: Calculate the potential energy at a height of 4 metres.**
The potential energy (PE) of an object at a certain height is given by the equation:
PE = mgh
where m is the mass of the object, g is the acceleration due to gravity, and h is the height.
Given:
m = 1 kg (mass of the stone)
g = 9.8 m/s² (acceleration due to gravity)
h = 4 m (height)
PE = (1 kg)(9.8 m/s²)(4 m) = 39.2 J
So, the potential energy of the stone at a height of 4 metres is 39.2 J.
**Step 2: Calculate the potential energy at a height of 1 metre.**
Using the same formula, we can calculate the potential energy at a height of 1 metre.
Given:
m = 1 kg (mass of the stone)
g = 9.8 m/s² (acceleration due to gravity)
h = 1 m (height)
PE = (1 kg)(9.8 m/s²)(1 m) = 9.8 J
So, the potential energy of the stone at a height of 1 metre is 9.8 J.
**Step 3: Calculate the kinetic energy at a height of 1 metre.**
The kinetic energy (KE) of an object is given by the equation:
KE = 0.5mv²
where m is the mass of the object and v is its velocity.
Since the stone is dropped from rest, its initial velocity is 0 m/s.
Given:
m = 1 kg (mass of the stone)
v = 0 m/s (initial velocity)
KE = 0.5(1 kg)(0 m/s)² = 0 J
So, the kinetic energy of the stone at a height of 1 metre is 0 J.
**Step 4: Calculate the total energy at a height of 1 metre.**
The total energy (TE) of an object is the sum of its potential energy and kinetic energy.
TE = PE + KE
TE = 9.8 J + 0 J = 9.8 J
So, the total energy of the stone at a height of 1 metre is 9.8 J.
Therefore, the correct answer is option B) 40 J.
When an object is dropped from a height, it undergoes free fall. During free fall, the only force acting on the object is the force of gravity. As the object falls, its potential energy is converted into kinetic energy.
**Step 1: Calculate the potential energy at a height of 4 metres.**
The potential energy (PE) of an object at a certain height is given by the equation:
PE = mgh
where m is the mass of the object, g is the acceleration due to gravity, and h is the height.
Given:
m = 1 kg (mass of the stone)
g = 9.8 m/s² (acceleration due to gravity)
h = 4 m (height)
PE = (1 kg)(9.8 m/s²)(4 m) = 39.2 J
So, the potential energy of the stone at a height of 4 metres is 39.2 J.
**Step 2: Calculate the potential energy at a height of 1 metre.**
Using the same formula, we can calculate the potential energy at a height of 1 metre.
Given:
m = 1 kg (mass of the stone)
g = 9.8 m/s² (acceleration due to gravity)
h = 1 m (height)
PE = (1 kg)(9.8 m/s²)(1 m) = 9.8 J
So, the potential energy of the stone at a height of 1 metre is 9.8 J.
**Step 3: Calculate the kinetic energy at a height of 1 metre.**
The kinetic energy (KE) of an object is given by the equation:
KE = 0.5mv²
where m is the mass of the object and v is its velocity.
Since the stone is dropped from rest, its initial velocity is 0 m/s.
Given:
m = 1 kg (mass of the stone)
v = 0 m/s (initial velocity)
KE = 0.5(1 kg)(0 m/s)² = 0 J
So, the kinetic energy of the stone at a height of 1 metre is 0 J.
**Step 4: Calculate the total energy at a height of 1 metre.**
The total energy (TE) of an object is the sum of its potential energy and kinetic energy.
TE = PE + KE
TE = 9.8 J + 0 J = 9.8 J
So, the total energy of the stone at a height of 1 metre is 9.8 J.
Therefore, the correct answer is option B) 40 J.
Smooth surface has less frictional force.- a)True
- b)False
Correct answer is option 'A'. Can you explain this answer?
Smooth surface has less frictional force.
a)
True
b)
False
|
|
Shruti Shaw answered |
Yes, smooth surfaces have less frictional force because they offer very less resistance while moving.
Force of friction depends on- a)Smoothness of surface
- b)Roughness of surface
- c)Inclination of surface
- d)All of above.
Correct answer is option 'D'. Can you explain this answer?
Force of friction depends on
a)
Smoothness of surface
b)
Roughness of surface
c)
Inclination of surface
d)
All of above.
|
Sanjana Bose answered |
Friction is the name given to the force that opposes the motion of one body sliding over another. It is called friction when the objects are solid, viscosity in liquids but it always opposes the motion of an object.
The first mathematical description was made by Charles Augustine de Coloumb in 1764. He proposed that friction could be classed as static or dynamic and proposed that the frictional force was frictional force dependent on the materials in contact.
Surface Contact
At an interface between two objects, the surfaces may appear to be smooth, however on a microscopic scale the surfaces are pitted and jagged.
The friction force depends on two factors:
a) The materials that are in contact. The two materials and the nature of their surfaces. Rougher surfaces have higher coefficient of frictions but to slide apart. This makes sense in terms of a model in which friction is described as arising from chemical bonds between the atoms of the two surfaces at their points of contact: very flat surfaces allow more atoms to come in contact
b) The force pushing the two surfaces together. Pushing the surfaces together causes the more of the asperities to come together and increases the surface area in contact with each other.
Soapy floor is slippery due to increased friction.- a)True
- b)False
Correct answer is option 'B'. Can you explain this answer?
Soapy floor is slippery due to increased friction.
a)
True
b)
False
|
Geetika Shah answered |
Soapy floor is slippery due to decreased friction. The soap covers the roughness of floor and makes it smooth, which restricts our walk on the floor.
So, the given statement is false.
So, the given statement is false.
In machine, friction between moving part is reduced by- a)Heating machine
- b)Using powder
- c)Using lubricants
- d)Using paints
Correct answer is option 'C'. Can you explain this answer?
In machine, friction between moving part is reduced by
a)
Heating machine
b)
Using powder
c)
Using lubricants
d)
Using paints
|
|
Ananya Das answered |
In machine, friction between moving parts is reduced by using lubricants. These lubricants stick with machine parts to make them smoother that leads to reduction in friction.
A lamp consumes 1000J of energy in 10s, what is its power?- a)100 W
- b)100000 W
- c)1k W
- d)1000 W
Correct answer is option 'A'. Can you explain this answer?
A lamp consumes 1000J of energy in 10s, what is its power?
a)
100 W
b)
100000 W
c)
1k W
d)
1000 W
|
|
Isha Isha answered |
Power =Work/time =1000 J /10 sec =100 WBecause SI unit of energy is watt .
Friction is a- a)contact force
- b)non-contact force
- c)magnetic force
- d)none of these.
Correct answer is option 'A'. Can you explain this answer?
Friction is a
a)
contact force
b)
non-contact force
c)
magnetic force
d)
none of these.
|
|
Rahul Negi answered |
The force which always opposes the motion of one body over another body frictional force. It acts between the two surfaces which are in contact with each other. Since frictional force arises when the surface of two objects are in touch with each other ,therefore, frictional force is an example of contact force.
Sprinkling of powder on the carrom board- a)Reduce friction
- b)Make the board durable
- c)Increase friction
- d)Maintain the friction
Correct answer is option 'A'. Can you explain this answer?
Sprinkling of powder on the carrom board
a)
Reduce friction
b)
Make the board durable
c)
Increase friction
d)
Maintain the friction
|
Siddharth Mukherjee answered |
Sliding friction is less than static friction. It is easier to move a heavy object by sliding in comparison to rotating on surface.
The frictional force exerted by fluids is also called- a)Drag
- b)Rung
- c)Smug
- d)Slag
Correct answer is option 'A'. Can you explain this answer?
The frictional force exerted by fluids is also called
a)
Drag
b)
Rung
c)
Smug
d)
Slag
|
Shraddha Menon answered |
The frictional force exerted by fluids is also called as drag. This kinds of frictional force can be reduced by changing the shape of the moving body.
Spring balance is a device used for measuring the force.- a)True
- b)False
Correct answer is option 'A'. Can you explain this answer?
Spring balance is a device used for measuring the force.
a)
True
b)
False
|
|
Manisha Shah answered |
Explanation:
A spring balance is a device that is used to measure the force exerted on an object. It consists of a spring fixed at one end and a hook at the other end. When a force is applied to the hook, the spring stretches and the amount of stretch is measured using a calibrated scale attached to the spring. The scale is usually marked in units of weight, such as pounds or kilograms.
How does it work?
The spring balance works on the principle of Hooke's Law, which states that the extension of a spring is proportional to the force applied to it. When a force is applied to the hook of the spring balance, the spring stretches and the amount of stretch is proportional to the force applied. This stretch is measured using a calibrated scale attached to the spring.
Uses of spring balance:
Spring balances are used in a variety of applications, including:
- Measuring the weight of an object
- Measuring the force required to compress or stretch a spring
- Measuring the force required to move an object
- Measuring the force required to pull or push an object
- Measuring the force required to lift an object
Advantages of spring balance:
- It is easy to use and does not require any complex setup or calibration
- It is relatively inexpensive compared to other types of force measuring devices
- It is portable and can be used in the field or in remote locations
- It is a non-destructive testing method and does not damage the object being tested
Conclusion:
Therefore, it can be concluded that the given statement "Spring balance is a device used for measuring the force" is true.
A spring balance is a device that is used to measure the force exerted on an object. It consists of a spring fixed at one end and a hook at the other end. When a force is applied to the hook, the spring stretches and the amount of stretch is measured using a calibrated scale attached to the spring. The scale is usually marked in units of weight, such as pounds or kilograms.
How does it work?
The spring balance works on the principle of Hooke's Law, which states that the extension of a spring is proportional to the force applied to it. When a force is applied to the hook of the spring balance, the spring stretches and the amount of stretch is proportional to the force applied. This stretch is measured using a calibrated scale attached to the spring.
Uses of spring balance:
Spring balances are used in a variety of applications, including:
- Measuring the weight of an object
- Measuring the force required to compress or stretch a spring
- Measuring the force required to move an object
- Measuring the force required to pull or push an object
- Measuring the force required to lift an object
Advantages of spring balance:
- It is easy to use and does not require any complex setup or calibration
- It is relatively inexpensive compared to other types of force measuring devices
- It is portable and can be used in the field or in remote locations
- It is a non-destructive testing method and does not damage the object being tested
Conclusion:
Therefore, it can be concluded that the given statement "Spring balance is a device used for measuring the force" is true.
Fluids are only liquids.- a)True
- b)False
Correct answer is option 'B'. Can you explain this answer?
Fluids are only liquids.
a)
True
b)
False
|
|
Shubham Sharma answered |
A fluid is a substance that continually flows under an applied shear stress, or external force. Fluids are a phase of matter and include liquids, gases, and plasmas.
So, the given statement is false.
So, the given statement is false.
Friction opposes the __________ between two surfaces in contact.- a)Reflective motion
- b)Relative motion
- c)Rotary motion
- d)Refractive motion
Correct answer is option 'B'. Can you explain this answer?
Friction opposes the __________ between two surfaces in contact.
a)
Reflective motion
b)
Relative motion
c)
Rotary motion
d)
Refractive motion
|
Tejas Iyer answered |
Friction opposes the relative motion between two surfaces in contact. Frictional force acts in opposite direction of motion to slow down the speed of moving body.
Irregularities between two surfaces interlock to produce friction.- a)True
- b)False
Correct answer is option 'A'. Can you explain this answer?
Irregularities between two surfaces interlock to produce friction.
a)
True
b)
False
|
Dipanjan Chaudhary answered |
Irregularities between two surfaces interlock to produce friction.
Explanation:
Friction is the force that opposes the relative motion or tendency of motion between two surfaces in contact. It is a result of the interlocking of irregularities between the surfaces. The irregularities or roughness on the surfaces create resistance, leading to the generation of frictional force. This statement is true and can be explained as follows:
1. Interlocking of irregularities:
When two surfaces come in contact, they may appear smooth at a macroscopic level, but at a microscopic level, they have irregularities or roughness. These irregularities can be in the form of bumps, ridges, or valleys on the surface. When the two surfaces are pressed together, these irregularities interlock with each other.
2. Contact points and friction:
The interlocking of irregularities creates contact points between the surfaces. These contact points are the areas where the surfaces are in direct contact with each other. Friction occurs at these contact points due to the resistance caused by the interlocking irregularities.
3. Resistance and frictional force:
As one surface attempts to slide or move relative to the other, the interlocking irregularities resist this motion. The irregularities act like tiny obstacles that need to be overcome. This resistance results in the generation of frictional force. The greater the irregularities and interlocking, the higher the frictional force.
4. Importance of friction:
Friction is an essential force in our daily lives. It allows us to walk, drive vehicles, grip objects, and perform various tasks. Without friction, objects would slide or slip uncontrollably. The interlocking of irregularities between surfaces provides the necessary grip and stability.
Therefore, the statement "Irregularities between two surfaces interlock to produce friction" is true. The interlocking of irregularities creates contact points and resistance, leading to the generation of frictional force.
Explanation:
Friction is the force that opposes the relative motion or tendency of motion between two surfaces in contact. It is a result of the interlocking of irregularities between the surfaces. The irregularities or roughness on the surfaces create resistance, leading to the generation of frictional force. This statement is true and can be explained as follows:
1. Interlocking of irregularities:
When two surfaces come in contact, they may appear smooth at a macroscopic level, but at a microscopic level, they have irregularities or roughness. These irregularities can be in the form of bumps, ridges, or valleys on the surface. When the two surfaces are pressed together, these irregularities interlock with each other.
2. Contact points and friction:
The interlocking of irregularities creates contact points between the surfaces. These contact points are the areas where the surfaces are in direct contact with each other. Friction occurs at these contact points due to the resistance caused by the interlocking irregularities.
3. Resistance and frictional force:
As one surface attempts to slide or move relative to the other, the interlocking irregularities resist this motion. The irregularities act like tiny obstacles that need to be overcome. This resistance results in the generation of frictional force. The greater the irregularities and interlocking, the higher the frictional force.
4. Importance of friction:
Friction is an essential force in our daily lives. It allows us to walk, drive vehicles, grip objects, and perform various tasks. Without friction, objects would slide or slip uncontrollably. The interlocking of irregularities between surfaces provides the necessary grip and stability.
Therefore, the statement "Irregularities between two surfaces interlock to produce friction" is true. The interlocking of irregularities creates contact points and resistance, leading to the generation of frictional force.
Fluids are- a)gases
- b)liquids
- c)gases and liquids both
- d)none of these.
Correct answer is option 'C'. Can you explain this answer?
Fluids are
a)
gases
b)
liquids
c)
gases and liquids both
d)
none of these.
|
Praneet Yadav answered |
In physics, a fluid is a substance that continually deforms under an applied shear stress. Fluids are a phases of matter and include liquids, gases and plasmas. Fluids are substances that have zero shear modulus, or, in simpler terms, a fluid is a substance which cannot resist any shear force applied to it.
Friction is a necessary evil.- a)True
- b)False
Correct answer is option 'A'. Can you explain this answer?
Friction is a necessary evil.
a)
True
b)
False
|
M Gj answered |
Friction is a necessary evil because there are many uses of friction in our lives but also there are some disadvantages like wearing out of tires.
So the answer is true.
Substances are called lubricants which are used to- a)increase friction
- b)decrease friction
- c)increase or decrease friction
- d)none of these.
Correct answer is option 'B'. Can you explain this answer?
Substances are called lubricants which are used to
a)
increase friction
b)
decrease friction
c)
increase or decrease friction
d)
none of these.
|
|
Ananya Das answered |
A lubricant is a substance, usually organic, introduced to reduce friction between surfaces in mutual contact, which ultimately reduces the heat generated when the surfaces move. It may also have the function of transmitting forces, transporting foreign particles, or heating or cooling the surfaces.
When we throw a rock from the top of a building which equation describes the energy of the body at each point during the fall?
- a)A
- b)B
- c)C
- d)D
Correct answer is option 'A'. Can you explain this answer?
When we throw a rock from the top of a building which equation describes the energy of the body at each point during the fall?
a)
A
b)
B
c)
C
d)
D
|
Mehak answered |
It's 'A ' because according to the law of conservation of energy , energy can only be transformed from to form to another , it can neither be created nor destroyed . The total energy before and after the transformation always remains constant.
The substance which reduce friction are called- a)Lubricants
- b)Wheels
- c)Powder
- d)Graphite
Correct answer is option 'A'. Can you explain this answer?
The substance which reduce friction are called
a)
Lubricants
b)
Wheels
c)
Powder
d)
Graphite
|
|
Ananya Das answered |
The substances which reduce friction are called lubricants. Lubricants include graphite, oils and greases. Lubricant stick with moving part to reduce friction.
What do ball bearings replace in most machines to reduce friction?
- a)Sliding friction
- b)Static friction
- c)Fluid friction
- d)Rolling friction
Correct answer is option 'A'. Can you explain this answer?
What do ball bearings replace in most machines to reduce friction?
a)
Sliding friction
b)
Static friction
c)
Fluid friction
d)
Rolling friction
|
Valor Academy answered |
Ball bearings replace sliding friction with rolling friction in most machines, which significantly reduces resistance and wear.
What happens to the contact points on a surface when an object starts sliding?- a)They interlock more
- b)They do not get enough time to interlock
- c)They become magnetic
- d)They disappear
Correct answer is option 'B'. Can you explain this answer?
a)
They interlock more
b)
They do not get enough time to interlock
c)
They become magnetic
d)
They disappear
|
L Rvi answered |
Friction
is caused by the interlocking of irregularities in the two surfaces. When the object starts sliding, the contact points on its surface, do not get enough time to lock into the contact points of the other surface.
The threaded tyres of cars, trucks and bus
- a)Decrease friction of ground
- b)Increase the velocity of vehicles
- c)Increase the diameter
- d)To increase friction and to give a better grip to them on the road
Correct answer is option 'D'. Can you explain this answer?
The threaded tyres of cars, trucks and bus
a)
Decrease friction of ground
b)
Increase the velocity of vehicles
c)
Increase the diameter
d)
To increase friction and to give a better grip to them on the road
|
Pooja Shah answered |
The treaded tyres of cars, trucks and bulldozers increase friction force between road and tyres and provide a better grip with the ground.
Friction is the resistance to motion of one object moving relative to another.
Friction is a resultant force not a fundamental one like the electromagnetic force.
Friction is the resistance to motion of one object moving relative to another.
Friction is a resultant force not a fundamental one like the electromagnetic force.
If a body moves on the sandy surface, its motion will
- a)Increase
- b)Decrease
- c)Neither increase nor decrease
- d)None of these
Correct answer is option 'B'. Can you explain this answer?
If a body moves on the sandy surface, its motion will
a)
Increase
b)
Decrease
c)
Neither increase nor decrease
d)
None of these
|
|
Kavya Mishra answered |
If a body moves on a sandy surface, its motion will generally decrease (option b).
This is because the sandy surface creates more friction and resistance compared to smoother surfaces, making it harder for the body to move. The increased friction slows down the body's motion.
Smooth surface has- a) less frictional force
- b) more frictional force
- c) sometimes less and sometimes more force
- d) all the above.
Correct answer is option 'A'. Can you explain this answer?
Smooth surface has
a)
less frictional force
b)
more frictional force
c)
sometimes less and sometimes more force
d)
all the above.
|
Shruti Choudhury answered |
**Explanation:**
**Friction** is the force that opposes the relative motion between two surfaces in contact. It acts tangentially to the surface and has two types: static friction and kinetic friction.
**Static friction** is the force that prevents a stationary object from moving when a force is applied to it. It is directly proportional to the force applied and can vary in magnitude. The maximum static friction force that can be exerted is given by the equation:
**fs ≤ µsN**
where fs is the static friction force, µs is the coefficient of static friction, and N is the normal force exerted on the object.
**Kinetic friction** is the force that opposes the sliding motion between two surfaces in contact. It is generally smaller than the maximum static friction force and is given by the equation:
**fk = µkN**
where fk is the kinetic friction force, µk is the coefficient of kinetic friction, and N is the normal force exerted on the object.
**Smooth surfaces** have a low coefficient of friction, meaning they have less resistance to motion and therefore experience less frictional force compared to rough surfaces.
Now, let's consider the options given:
**a) Less frictional force:** Smooth surfaces have less frictional force because their coefficients of friction (both static and kinetic) are low. This means that it is easier for objects to slide or move on smooth surfaces with less resistance.
**b) More frictional force:** This option is incorrect because, as mentioned above, smooth surfaces have less frictional force due to their low coefficients of friction.
**c) Sometimes less and sometimes more force:** This option is incorrect because smooth surfaces consistently have less frictional force compared to rough surfaces.
**d) All of the above:** This option is incorrect as well because only option 'a' is correct.
Therefore, the correct answer is option 'A', smooth surfaces have less frictional force.
**Friction** is the force that opposes the relative motion between two surfaces in contact. It acts tangentially to the surface and has two types: static friction and kinetic friction.
**Static friction** is the force that prevents a stationary object from moving when a force is applied to it. It is directly proportional to the force applied and can vary in magnitude. The maximum static friction force that can be exerted is given by the equation:
**fs ≤ µsN**
where fs is the static friction force, µs is the coefficient of static friction, and N is the normal force exerted on the object.
**Kinetic friction** is the force that opposes the sliding motion between two surfaces in contact. It is generally smaller than the maximum static friction force and is given by the equation:
**fk = µkN**
where fk is the kinetic friction force, µk is the coefficient of kinetic friction, and N is the normal force exerted on the object.
**Smooth surfaces** have a low coefficient of friction, meaning they have less resistance to motion and therefore experience less frictional force compared to rough surfaces.
Now, let's consider the options given:
**a) Less frictional force:** Smooth surfaces have less frictional force because their coefficients of friction (both static and kinetic) are low. This means that it is easier for objects to slide or move on smooth surfaces with less resistance.
**b) More frictional force:** This option is incorrect because, as mentioned above, smooth surfaces have less frictional force due to their low coefficients of friction.
**c) Sometimes less and sometimes more force:** This option is incorrect because smooth surfaces consistently have less frictional force compared to rough surfaces.
**d) All of the above:** This option is incorrect as well because only option 'a' is correct.
Therefore, the correct answer is option 'A', smooth surfaces have less frictional force.
The shape of fish is streamlined to- a)Change the direction
- b)Increase fluid friction
- c)Facilitate breathing
- d)Decrease fluid friction
Correct answer is option 'D'. Can you explain this answer?
The shape of fish is streamlined to
a)
Change the direction
b)
Increase fluid friction
c)
Facilitate breathing
d)
Decrease fluid friction
|
Sumit Bansal answered |
This is because when a object is streamlined it cuts the upon itself by fluids through streamline shape
What is a spring balance used for?- a)Measuring weight
- b)Measuring mass
- c)Measuring force
- d)Measuring speed
Correct answer is option 'C'. Can you explain this answer?
What is a spring balance used for?
a)
Measuring weight
b)
Measuring mass
c)
Measuring force
d)
Measuring speed
|
EduRev Class 8 answered |
A spring balance is used for measuring force.
- Working Principle: It operates on Hooke's Law, which states that the force exerted by a spring is directly proportional to the displacement of the spring.
- Usage: When an object is attached, the spring stretches, and the amount of stretch correlates with the force applied, which is often related to the object's weight.
- Units: Typically measures force in newtons (N).
Hence, the correct answer is C: Measuring force.
- Working Principle: It operates on Hooke's Law, which states that the force exerted by a spring is directly proportional to the displacement of the spring.
- Usage: When an object is attached, the spring stretches, and the amount of stretch correlates with the force applied, which is often related to the object's weight.
- Units: Typically measures force in newtons (N).
Hence, the correct answer is C: Measuring force.
Why is it easier to move a box already in motion than to start moving it?- a)Less gravitational force
- b)Less static friction
- c)More kinetic energy
- d)Less air resistance
Correct answer is option 'B'. Can you explain this answer?
a)
Less gravitational force
b)
Less static friction
c)
More kinetic energy
d)
Less air resistance
|
|
Mehul Malik answered |
Understanding Friction in Motion
Moving a box requires overcoming forces that resist its movement. The primary reason it is easier to move a box already in motion than to start moving it is due to the differences in frictional forces involved.
Types of Friction
- Static Friction: This is the friction that must be overcome to start moving an object at rest. It is usually higher than kinetic friction.
- Kinetic Friction: Once the object is in motion, it experiences kinetic friction, which is generally lower than static friction.
Why is Option B Correct?
- Less Static Friction: When an object is stationary, static friction acts to keep it at rest. This force can be significant and varies depending on the materials in contact. It requires a greater applied force to overcome this static friction and initiate movement.
- Once in Motion: Once the box is moving, it transitions to kinetic friction. Kinetic friction is easier to overcome because it is less than static friction.
Implications of Kinetic Energy
- Energy Considerations: An object in motion has kinetic energy, which means it will continue to move unless acted upon by another force. Thus, once the box is in motion, it requires less energy to maintain that motion compared to the energy needed to start it.
Conclusion
In summary, the reason it is easier to move a box already in motion than to start moving it is primarily due to the lower kinetic friction that acts on a moving object compared to the higher static friction that must be overcome to initiate movement.
Moving a box requires overcoming forces that resist its movement. The primary reason it is easier to move a box already in motion than to start moving it is due to the differences in frictional forces involved.
Types of Friction
- Static Friction: This is the friction that must be overcome to start moving an object at rest. It is usually higher than kinetic friction.
- Kinetic Friction: Once the object is in motion, it experiences kinetic friction, which is generally lower than static friction.
Why is Option B Correct?
- Less Static Friction: When an object is stationary, static friction acts to keep it at rest. This force can be significant and varies depending on the materials in contact. It requires a greater applied force to overcome this static friction and initiate movement.
- Once in Motion: Once the box is moving, it transitions to kinetic friction. Kinetic friction is easier to overcome because it is less than static friction.
Implications of Kinetic Energy
- Energy Considerations: An object in motion has kinetic energy, which means it will continue to move unless acted upon by another force. Thus, once the box is in motion, it requires less energy to maintain that motion compared to the energy needed to start it.
Conclusion
In summary, the reason it is easier to move a box already in motion than to start moving it is primarily due to the lower kinetic friction that acts on a moving object compared to the higher static friction that must be overcome to initiate movement.
Friction always- a)helps the motion
- b)opposes the motion
- c)both of these
- d)none of these.
Correct answer is option 'B'. Can you explain this answer?
Friction always
a)
helps the motion
b)
opposes the motion
c)
both of these
d)
none of these.
|
Deebyajyoti answered |
The force which opposes the motion of an object is called frictional force and frictional force always act in a direction opposite to the direction of motion of the object.
What increases the force of friction between two surfaces?- a)Decreasing pressure
- b)Increasing pressure
- c)Reducing contact area
- d)Reducing surface area
Correct answer is option 'B'. Can you explain this answer?
a)
Decreasing pressure
b)
Increasing pressure
c)
Reducing contact area
d)
Reducing surface area
|
Master Training Institute answered |
Increasing the pressure between two surfaces increases the interlocking of irregularities, thereby increasing friction.
What is the effect of friction when a jar of a mixer is operated?- a)It increases speed
- b)It reduces efficiency
- c)It generates heat
- d)It decreases weight
Correct answer is option 'C'. Can you explain this answer?
a)
It increases speed
b)
It reduces efficiency
c)
It generates heat
d)
It decreases weight
|
Lohit Matani answered |
Friction between the moving parts generates heat, causing the jar of the mixer to become hot.
Objects moving through fluids experience _______ force.- a)Magnetic
- b)Gravitational
- c)Frictional
- d)Elastic
Correct answer is option 'C'. Can you explain this answer?
Objects moving through fluids experience _______ force.
a)
Magnetic
b)
Gravitational
c)
Frictional
d)
Elastic
|
S.S Career Academy answered |
When objects move through fluids like air or water, they experience a force called frictional force. This force makes it harder for objects to move smoothly through the fluid.
Friction is a/an- a)Friend
- b)Foe
- c)Both (a) and (b)
- d)None.
Correct answer is option 'C'. Can you explain this answer?
Friction is a/an
a)
Friend
b)
Foe
c)
Both (a) and (b)
d)
None.
|
Meera Basu answered |
Friction is both friend as well as foe.
Friend:- as friction helps us to write, walk to control our speed .
Foe:- as it cause wear and tear in object.
So, friction is both Friend and foe.
Friend:- as friction helps us to write, walk to control our speed .
Foe:- as it cause wear and tear in object.
So, friction is both Friend and foe.
We slip while walking on a path having pond scum or green algae because: - a)The inertia of motion
- b)The friction is zero
- c)The friction between the feet and the path is increased.
- d)The friction between the feet and the path is reduced.
Correct answer is option 'D'. Can you explain this answer?
We slip while walking on a path having pond scum or green algae because:
a)
The inertia of motion
b)
The friction is zero
c)
The friction between the feet and the path is increased.
d)
The friction between the feet and the path is reduced.
|
Shanaya Menon answered |
Why we slip while walking on a path with pond scum or green algae?
The correct answer is option 'D', which states that the friction between the feet and the path is reduced. Let's understand why this is the correct answer in detail.
The concept of friction:
Friction is the force that opposes the relative motion between two surfaces in contact. It plays a crucial role in our daily lives, allowing us to walk, hold objects, and perform various tasks requiring grip.
Factors affecting friction:
Friction depends on several factors, including the nature of the surfaces in contact and the force pressing them together. When there is an increase in the roughness of the surfaces or an increase in the force pressing them together, the friction between the surfaces also increases.
Effect of pond scum or green algae on friction:
When we walk on a path covered with pond scum or green algae, the surface becomes slimy and slippery. This slimy layer reduces the friction between our feet and the path, making it easier for us to slip.
1. Reduction in surface roughness: Pond scum or green algae create a slimy layer on the path, which reduces the roughness of the surface. The slimy layer acts as a lubricant, making it difficult for our feet to grip onto the surface.
2. Reduction in force pressing the surfaces together: As we step on the slimy surface, the force pressing our feet against the path decreases due to the lubricating effect of the pond scum or green algae. This reduced force diminishes the friction between our feet and the path, further increasing the chances of slipping.
Consequences of reduced friction:
When the friction between our feet and the path is reduced, we experience a lack of grip and stability. This can lead to slipping and loss of balance, which can cause falls, injuries, and accidents.
In summary, the presence of pond scum or green algae on a path reduces the friction between our feet and the surface. The slimy layer acts as a lubricant, decreasing the surface roughness and the force pressing the surfaces together. This reduction in friction makes it easier for us to slip while walking on such a path.
The correct answer is option 'D', which states that the friction between the feet and the path is reduced. Let's understand why this is the correct answer in detail.
The concept of friction:
Friction is the force that opposes the relative motion between two surfaces in contact. It plays a crucial role in our daily lives, allowing us to walk, hold objects, and perform various tasks requiring grip.
Factors affecting friction:
Friction depends on several factors, including the nature of the surfaces in contact and the force pressing them together. When there is an increase in the roughness of the surfaces or an increase in the force pressing them together, the friction between the surfaces also increases.
Effect of pond scum or green algae on friction:
When we walk on a path covered with pond scum or green algae, the surface becomes slimy and slippery. This slimy layer reduces the friction between our feet and the path, making it easier for us to slip.
1. Reduction in surface roughness: Pond scum or green algae create a slimy layer on the path, which reduces the roughness of the surface. The slimy layer acts as a lubricant, making it difficult for our feet to grip onto the surface.
2. Reduction in force pressing the surfaces together: As we step on the slimy surface, the force pressing our feet against the path decreases due to the lubricating effect of the pond scum or green algae. This reduced force diminishes the friction between our feet and the path, further increasing the chances of slipping.
Consequences of reduced friction:
When the friction between our feet and the path is reduced, we experience a lack of grip and stability. This can lead to slipping and loss of balance, which can cause falls, injuries, and accidents.
In summary, the presence of pond scum or green algae on a path reduces the friction between our feet and the surface. The slimy layer acts as a lubricant, decreasing the surface roughness and the force pressing the surfaces together. This reduction in friction makes it easier for us to slip while walking on such a path.
Why do we slip when we step on a banana peel?- a)Increased gravitational pull
- b)Reduced friction
- c)Increased air resistance
- d)Reduced weight
Correct answer is option 'B'. Can you explain this answer?
a)
Increased gravitational pull
b)
Reduced friction
c)
Increased air resistance
d)
Reduced weight
|
Academic Studio answered |
The banana peel reduces the friction between our feet and the ground, making it easier to slip.
What helps increase the grip of a shoe on the floor?- a)Smooth soles
- b)Grooved soles
- c)Thin soles
- d)Heavy soles
Correct answer is option 'B'. Can you explain this answer?
a)
Smooth soles
b)
Grooved soles
c)
Thin soles
d)
Heavy soles
|
Prasad Basu answered |
Importance of Shoe Grip
The grip of a shoe is crucial for stability and safety during movement. A shoe with good grip helps prevent slips and falls, enhancing overall performance.
Key Characteristics of Grooved Soles
- Enhanced Traction: Grooved soles feature patterns that create channels for better surface contact. These grooves allow the shoe to grip uneven or slippery surfaces more effectively.
- Water Dispersion: The grooves in the sole help in channeling away water, which reduces hydroplaning. This is particularly beneficial in wet conditions, as it enhances traction.
- Flexibility: Grooved soles can flex and adapt to the surface, providing better grip on various terrains. This flexibility allows for improved balance and control.
Comparison with Other Sole Types
- Smooth Soles: These offer minimal friction and are more likely to slip on slick surfaces, providing poor grip.
- Thin Soles: While they may be lightweight, thin soles typically lack the necessary surface area and traction features, leading to decreased grip.
- Heavy Soles: Although weight can contribute to stability, heavy soles do not inherently improve grip and may hinder agility.
Conclusion
In summary, grooved soles significantly enhance the grip of shoes by providing better traction, water management, and flexibility. Choosing shoes with these features is essential for ensuring safety and performance, especially in challenging environments.
The grip of a shoe is crucial for stability and safety during movement. A shoe with good grip helps prevent slips and falls, enhancing overall performance.
Key Characteristics of Grooved Soles
- Enhanced Traction: Grooved soles feature patterns that create channels for better surface contact. These grooves allow the shoe to grip uneven or slippery surfaces more effectively.
- Water Dispersion: The grooves in the sole help in channeling away water, which reduces hydroplaning. This is particularly beneficial in wet conditions, as it enhances traction.
- Flexibility: Grooved soles can flex and adapt to the surface, providing better grip on various terrains. This flexibility allows for improved balance and control.
Comparison with Other Sole Types
- Smooth Soles: These offer minimal friction and are more likely to slip on slick surfaces, providing poor grip.
- Thin Soles: While they may be lightweight, thin soles typically lack the necessary surface area and traction features, leading to decreased grip.
- Heavy Soles: Although weight can contribute to stability, heavy soles do not inherently improve grip and may hinder agility.
Conclusion
In summary, grooved soles significantly enhance the grip of shoes by providing better traction, water management, and flexibility. Choosing shoes with these features is essential for ensuring safety and performance, especially in challenging environments.
In winters, rubbing of hands together for some time, causes a sensation of warmth mainly because of - a)heat caused by the force of friction
- b)heat caused by the momentum
- c)heat caused by the motion
- d)heat flows from the blood to skin
Correct answer is option 'A'. Can you explain this answer?
In winters, rubbing of hands together for some time, causes a sensation of warmth mainly because of
a)
heat caused by the force of friction
b)
heat caused by the momentum
c)
heat caused by the motion
d)
heat flows from the blood to skin
|
|
Ravi Verma answered |
If you rub your hands together for several seconds, you'll notice that your hands feel warm. That warmth is caused by a force called friction. When objects like your hands come in contact and move against each other, they produce friction. Friction happens when you overcome the resistance of one object rubbing against the other. The force of the friction is opposes the direction of the motion. If you just put your hands together, there's no resistance, so there's no friction produced. Rub them together and there's friction.
What does the reading on a spring balance indicate when a brick begins to move?- a)Weight of the brick
- b)Force of friction
- c)Mass of the brick
- d)Gravitational force
Correct answer is option 'B'. Can you explain this answer?
a)
Weight of the brick
b)
Force of friction
c)
Mass of the brick
d)
Gravitational force
|
Upsc Rank Holders answered |
The reading on the spring balance gives a measure of the force of friction between the brick and the floor when the brick just begins to move.
If work is done at a faster rate, then- a)power is more
- b)No power is required to do work
- c)power is less
- d)Infinite power is required
Correct answer is option 'A'. Can you explain this answer?
If work is done at a faster rate, then
a)
power is more
b)
No power is required to do work
c)
power is less
d)
Infinite power is required
|
|
Anirudh Choudhury answered |
Explanation:
In order to understand why power is more when work is done at a faster rate, it is important to first understand the concept of power and its relation to work.
Power:
Power is the rate at which work is done or energy is transferred. It is defined as the amount of work done per unit time. Mathematically, power can be expressed as:
Power = Work / Time
Work:
Work is the transfer of energy that occurs when a force is applied to an object and the object is displaced. It is given by the formula:
Work = Force x Displacement x cos(angle)
Relation between Power and Work:
From the formula for power, we can see that power is directly proportional to work. This means that when more work is done, the power is greater. Similarly, when less work is done, the power is less. Therefore, if work is done at a faster rate, it means that more work is being done in a given amount of time, resulting in greater power.
Example:
Let's consider an example to illustrate this concept. Suppose two people are lifting the same object to the same height. The first person takes 10 seconds to lift the object, while the second person takes only 5 seconds to lift the same object to the same height. Both individuals are doing the same amount of work (assuming the force applied and displacement are the same), but the second person is doing the work at a faster rate than the first person. Therefore, the second person has a higher power output compared to the first person.
Conclusion:
In conclusion, when work is done at a faster rate, power is more. This is because power is directly proportional to the amount of work done, and when work is done more quickly, more work is done in a given amount of time, resulting in a higher power output.
In order to understand why power is more when work is done at a faster rate, it is important to first understand the concept of power and its relation to work.
Power:
Power is the rate at which work is done or energy is transferred. It is defined as the amount of work done per unit time. Mathematically, power can be expressed as:
Power = Work / Time
Work:
Work is the transfer of energy that occurs when a force is applied to an object and the object is displaced. It is given by the formula:
Work = Force x Displacement x cos(angle)
Relation between Power and Work:
From the formula for power, we can see that power is directly proportional to work. This means that when more work is done, the power is greater. Similarly, when less work is done, the power is less. Therefore, if work is done at a faster rate, it means that more work is being done in a given amount of time, resulting in greater power.
Example:
Let's consider an example to illustrate this concept. Suppose two people are lifting the same object to the same height. The first person takes 10 seconds to lift the object, while the second person takes only 5 seconds to lift the same object to the same height. Both individuals are doing the same amount of work (assuming the force applied and displacement are the same), but the second person is doing the work at a faster rate than the first person. Therefore, the second person has a higher power output compared to the first person.
Conclusion:
In conclusion, when work is done at a faster rate, power is more. This is because power is directly proportional to the amount of work done, and when work is done more quickly, more work is done in a given amount of time, resulting in a higher power output.
A ball is thrown vertically upwards. Its velocity keeps on decreasing. What happens to its kinetic energy when its reaches the maximum height?- a)Kinetic energy is double
- b)Kinetic energy is zero
- c)Kinetic energy is maximum at maximum height
- d)Kinetic energy is half of initial value
Correct answer is option 'B'. Can you explain this answer?
A ball is thrown vertically upwards. Its velocity keeps on decreasing. What happens to its kinetic energy when its reaches the maximum height?
a)
Kinetic energy is double
b)
Kinetic energy is zero
c)
Kinetic energy is maximum at maximum height
d)
Kinetic energy is half of initial value
|
Tanu Choudhary.sweetu. answered |
When is reaches at height it's kinetic energy is transformed into potential energy. .. . ....because the changing in size and shape and position of body is called potential energy.....so here energy is transformed....
Friction increases with increase in the smoothness of the surface.- a)True
- b)False
Correct answer is option 'B'. Can you explain this answer?
Friction increases with increase in the smoothness of the surface.
a)
True
b)
False
|
Nancy yadav answered |
It's answer is false because as the smoothness increases friction decreases
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