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All questions of Work and Energy for Class 9 Exam
A coolie was standing with 2 suitcases on his head and 2 bags in his hand. The luggage exerted a force of 159 N on him. What is the amount of work done by him?- a)79.5 J
- b)318 J
- c)0 J
- d)159 J
Correct answer is option 'C'. Can you explain this answer?
A coolie was standing with 2 suitcases on his head and 2 bags in his hand. The luggage exerted a force of 159 N on him. What is the amount of work done by him?
a)
79.5 J
b)
318 J
c)
0 J
d)
159 J
 | Ananya Das answered |
Work done is zero, since there is no displacement of the coolie.
Calculate the distance between the man and the box when the work done to move the box was 100 J with a force of 15 N.- a)6 m
- b)16.6 m
- c)26.6 m
- d)6.6 m
Correct answer is option 'D'. Can you explain this answer?
Calculate the distance between the man and the box when the work done to move the box was 100 J with a force of 15 N.
a)
6 m
b)
16.6 m
c)
26.6 m
d)
6.6 m
 | Raghav Bansal answered |
As given, W = 100 J, F = 15 N
We know, W = Fs
⇒ s = W/ F
⇒ s = 100 / 15
⇒ s = 6.6 m
We know, W = Fs
⇒ s = W/ F
⇒ s = 100 / 15
⇒ s = 6.6 m
Newton-metre is the unit of- a)power
- b)work
- c)momentum
- d)gravitational intensity
Correct answer is option 'B'. Can you explain this answer?
Newton-metre is the unit of
a)
power
b)
work
c)
momentum
d)
gravitational intensity
 | Swati Verma answered |
Work=Force*Displacement (N-m)
Can you explain the answer of this question below:A force a body of mass 3 kg producing a displacement of 10 m in it. The work done by force is of 6 N acts on
- A:
30 J
- B:
60 J
- C:
18 J
- D:
36 J
The answer is a.
A force a body of mass 3 kg producing a displacement of 10 m in it. The work done by force is of 6 N acts on
30 J
60 J
18 J
36 J
 | Sonal Sinha answered |
Here,
work done(W)=fdcos60degree
W=6×10×1/2
w=60/2
w=30j(Ans).
work done(W)=fdcos60degree
W=6×10×1/2
w=60/2
w=30j(Ans).
To lift 700 kg of water, through a height of 10 m we use a pump. The work done in operating the pump is;
Take g = 10 m/s2.- a)7 kilo joules
- b)7 x 106 J
- c)700 J
- d)70000 J
Correct answer is option 'D'. Can you explain this answer?
To lift 700 kg of water, through a height of 10 m we use a pump. The work done in operating the pump is;
Take g = 10 m/s2.
Take g = 10 m/s2.
a)
7 kilo joules
b)
7 x 106 J
c)
700 J
d)
70000 J
| | Amit Sharma answered |
Work done = mgh
= 700 kg x 10m/s x 10m = 70000 joule
= 700 kg x 10m/s x 10m = 70000 joule
How fast should a person with mass 50kg walk so that his kinetic energy is 625 J ?- a)15 km/s
- b)0.5 m/s
- c)5 m/s
- d)5 Km/s
Correct answer is option 'C'. Can you explain this answer?
How fast should a person with mass 50kg walk so that his kinetic energy is 625 J ?
a)
15 km/s
b)
0.5 m/s
c)
5 m/s
d)
5 Km/s
 | Soumya answered |
K.E = 0.5mv²
v = √(2K.E / m)
= √(2 × 625 Joule / 50 kg)
= √(625 Joule / 25 kg)
= 5 m/s...
v = √(2K.E / m)
= √(2 × 625 Joule / 50 kg)
= √(625 Joule / 25 kg)
= 5 m/s...
The winners of long jump each weighing 56 Kg, 40 Kg and 45 Kg stand on the podium. What is the work done by them on the podium while they receive the medals?- a)250 J
- b)0 J
- c)282 J
- d)141 J
Correct answer is option 'B'. Can you explain this answer?
The winners of long jump each weighing 56 Kg, 40 Kg and 45 Kg stand on the podium. What is the work done by them on the podium while they receive the medals?
a)
250 J
b)
0 J
c)
282 J
d)
141 J
| | Aayush Kumar answered |
The winners of long jump each weighing 56kg,40kg and 45 kg stand on podium.Work done by them is 0 Ioule because there is no displacement and if the displacement is 0 then work done will be also 0.
Two bodies of unequal masses are dropped from a cliff. At any instant, they have equal- a)momentum
- b)acceleration
- c)potential energy
- d)kinetic energy
Correct answer is option 'B'. Can you explain this answer?
Two bodies of unequal masses are dropped from a cliff. At any instant, they have equal
a)
momentum
b)
acceleration
c)
potential energy
d)
kinetic energy
| | Anita Menon answered |
They will have the same acceleration due to gravity because it is independent of mass.
Work done by a body is- a)negative, positive or zero
- b)always positive
- c)always zero
- d)always negative
Correct answer is option 'A'. Can you explain this answer?
Work done by a body is
a)
negative, positive or zero
b)
always positive
c)
always zero
d)
always negative
| | Anita Menon answered |
Positive Work
- If a force displaces the object in its direction, then the work done is positive
So, W=Fd
The example of this kind of work done is motion of ball falling towards ground where displacement of ball is in the direction of force of gravity.
Negative work
- If the force and the displacement are in opposite directions, then the work is said to be negative. For example if a ball is thrown in upwards direction, its displacement would be in upwards direction but the force due to earth’s gravity is in the downward direction.
So here in this case gravity is doing negative work when you throw the ball upwards. Hence the work done by gravitational force is negative. Mathematically when displacement is opposite to the force work done is given by
- Negative work just means that the force and the displacement act in opposite directions.
Case of zero work done
- If the directions of force and the displacement are perpendicular to each other, the work done by the force on the object is zero.
For example, when we push hard against a wall, the force we are exerting on the wall does no work, because in this case the displacement of the wall is d = 0. However, in this process, our muscles are using our internal energy and as a result we get tired.
A body of mass 5 kg is moving with an acceleration of 5 ms-2 gets a displacement of 2m, the work done by the force is:- a)75 J
- b)25 J
- c)100 J
- d)50 J
Correct answer is option 'D'. Can you explain this answer?
A body of mass 5 kg is moving with an acceleration of 5 ms-2 gets a displacement of 2m, the work done by the force is:
a)
75 J
b)
25 J
c)
100 J
d)
50 J
 | Vikas Kapoor answered |
We know, F = ma
F = 5 * 5
F = 25
We, also know;
W = F. s
= 25 * 2
W = 50 J
F = 5 * 5
F = 25
We, also know;
W = F. s
= 25 * 2
W = 50 J
Scientifically, work is said to be done in which of the following cases- a)Manish pulls the trolley for a certain distance
- b)Mira studies for her exam
- c)Manoj pushes the wall with no change in the position of wall
- d)Mira pulls the wall with no change in the position of wall
Correct answer is option 'A'. Can you explain this answer?
Scientifically, work is said to be done in which of the following cases
a)
Manish pulls the trolley for a certain distance
b)
Mira studies for her exam
c)
Manoj pushes the wall with no change in the position of wall
d)
Mira pulls the wall with no change in the position of wall
 | Mohit Rajpoot answered |
Manish pulls the trolley for a certain distance:- force is applied and there is displacement also , so work is done.
A flying aeroplane possesses- a)only potential energy
- b)only kinetic energy
- c)both potential and kinetic energy
- d)neither potential nor kinetic energy
Correct answer is option 'C'. Can you explain this answer?
A flying aeroplane possesses
a)
only potential energy
b)
only kinetic energy
c)
both potential and kinetic energy
d)
neither potential nor kinetic energy
| | Rajat Singh answered |
Correct answer is option c because it is flying above ground level it will posses potential energy and since it is moving with the motion associated through it, it possesses kinetic energy.
Calculate the work done in moving a body of mass 50 Kg through a height of 5 m.(g = 10m/s2)- a)250 J
- b)2500 J
- c)25 x 103 J
- d)2.5 x 105 J
Correct answer is option 'B'. Can you explain this answer?
Calculate the work done in moving a body of mass 50 Kg through a height of 5 m.(g = 10m/s2)
a)
250 J
b)
2500 J
c)
25 x 103 J
d)
2.5 x 105 J
 | Sonal Sinha answered |
W=fd
Force=mg =50×10=500N
W=fd
=500×5=2500j(Ans).
Force=mg =50×10=500N
W=fd
=500×5=2500j(Ans).
A freely falling body during its fall will have- a)Kinetic energy
- b)Potential energy
- c)Sound energy
- d)Both kinetic energy and potential energy
Correct answer is option 'D'. Can you explain this answer?
A freely falling body during its fall will have
a)
Kinetic energy
b)
Potential energy
c)
Sound energy
d)
Both kinetic energy and potential energy
 | Jyoti Kapoor answered |
Object Falling from Rest. As an object falls from rest, its gravitational potential energy is converted to kinetic energy. Conservation of energy as a tool permits the calculation of the velocity just before it hits the surface. K.E. = J, which is of course equal to its initial potential energy.
Can you explain the answer of this question below:A certain household has consumed 250 units of energy during a month. How much energy is this in joules?
- A:
9 ×106J
- B:
5 × 108 Joule
- C:
10 × 105Joule
- D:
9 ×108J
The answer is d.
A certain household has consumed 250 units of energy during a month. How much energy is this in joules?
9 ×106J
5 × 108 Joule
10 × 105Joule
9 ×108J
| | Sarita Reddy answered |
1 unit of energy is equal to 1 kilowatt hour (kWh).
1 unit = 1 kWh
1 kWh = 3.6 x 10^6J
Therefore, 250 units of energy = 250 x 3.6 x 10^6 = 9 x 10^8 J.
Two masses m and 2m are dropped from certain height ‘h’. Then on reaching the ground,- a)K.E. of them will be equal
- b)K.E. of the heavier is 4 times the K.E. of the lighter
- c)K.E. of the lighter is 4 times the K.E. of the heavier
- d)K.E. of the heavier is more than that of the lighter.
Correct answer is option 'D'. Can you explain this answer?
Two masses m and 2m are dropped from certain height ‘h’. Then on reaching the ground,
a)
K.E. of them will be equal
b)
K.E. of the heavier is 4 times the K.E. of the lighter
c)
K.E. of the lighter is 4 times the K.E. of the heavier
d)
K.E. of the heavier is more than that of the lighter.
| | Swati Verma answered |
- Since the free-falling acceleration is not dependent on mass, the final velocities of both masses are the same.
The kinetic energy = KE = mv2/2 - Hence, the kinetic energy of the heavier mass will be more.
If the velocity of a moving car is halved, its kinetic energy would- a)Double
- b)Become Half
- c)Become one fourth
- d)Remain same
Correct answer is option 'C'. Can you explain this answer?
If the velocity of a moving car is halved, its kinetic energy would
a)
Double
b)
Become Half
c)
Become one fourth
d)
Remain same
 | Krishna Iyer answered |
Kinetic Energy = (1/2) mv2.
If the velocity of a body is halved, its kinetic energy becomes one fourth as kinetic energy is directly proportional to velocity squared.
If 1 newton of force displaces a body by 1 m, the work done is- a)10 joule
- b)5 joule
- c)1 joule
- d)Depends on time
Correct answer is option 'C'. Can you explain this answer?
If 1 newton of force displaces a body by 1 m, the work done is
a)
10 joule
b)
5 joule
c)
1 joule
d)
Depends on time
| | Prasad Ghoshal answered |
Explanation:
Work done is defined as the product of force and displacement in the direction of force. Thus, if 1 newton of force displaces a body by 1 m, the work done will be:
Work = Force x Displacement
= 1 N x 1 m
= 1 joule
Therefore, the correct answer is option 'C'.
Work done is defined as the product of force and displacement in the direction of force. Thus, if 1 newton of force displaces a body by 1 m, the work done will be:
Work = Force x Displacement
= 1 N x 1 m
= 1 joule
Therefore, the correct answer is option 'C'.
If two bodies of different masses have the same K.E. then the relation between momentum and mass will be:- a)
- b)
- c)
- d)
Correct answer is option 'D'. Can you explain this answer?
If two bodies of different masses have the same K.E. then the relation between momentum and mass will be:
a)
b)
c)
d)
 | Shiksha Academy answered |
KE = K = 1 /2( mv2)
We know, p = mv
⇒ K = p2 / 2m
p2 = 2Km
As, KE is Same, ie . Constant, momentum would be directly proportional to the square root of mass.
We know, p = mv
⇒ K = p2 / 2m
p2 = 2Km
As, KE is Same, ie . Constant, momentum would be directly proportional to the square root of mass.
Potential energy is energy possessed by an object due to its- a)motion
- b)speed
- c)position
- d)None of these
Correct answer is option 'C'. Can you explain this answer?
Potential energy is energy possessed by an object due to its
a)
motion
b)
speed
c)
position
d)
None of these
| | Aayush Kumar answered |
Potential energy is energy possessed by an object due to its position,shape or size.
A body at rest cannot have:- a)potential energy
- b)kinetic energy
- c)Electrical energy
- d)Both A and B
Correct answer is option 'B'. Can you explain this answer?
A body at rest cannot have:
a)
potential energy
b)
kinetic energy
c)
Electrical energy
d)
Both A and B
 | Khushi Gupta answered |
Because kinetic energy = 1/2 mv^2
And if it is at rest , then there is no velocity
so by putting the value of v in the formula,
we get zero .
So we find that a body possesses no kinetic energy when at rest...
And if it is at rest , then there is no velocity
so by putting the value of v in the formula,
we get zero .
So we find that a body possesses no kinetic energy when at rest...
A fish with weight 35 kg dives and hits the ground (zero height) with kinetic energy equal to 3500J. Find the height through which fish dived. Take g = 10 m/s2- a)1 km
- b)100 m
- c)10 m
- d)20 m
Correct answer is option 'C'. Can you explain this answer?
A fish with weight 35 kg dives and hits the ground (zero height) with kinetic energy equal to 3500J. Find the height through which fish dived. Take g = 10 m/s2
a)
1 km
b)
100 m
c)
10 m
d)
20 m
| | Ananya Das answered |
We can use the principle of conservation of mechanical energy to solve this problem. According to this principle, the potential energy (PE) at the height is converted into kinetic energy (KE) as the fish dives to the ground.
The formula for potential energy is:
PE=mgh
Where:
- m=35 kg
- g=10 m/s^2
- hhh is the height through which the fish dived (which we need to find)
Given that the kinetic energy when the fish hits the ground is equal to the potential energy it had at the starting height:
KE=PE
3500 J=35×10×h
Now solve for h:
3500=350h
h=3500/350=10 m
So, the height through which the fish dived is 10 meters.
The correct answer is:
3. 10 m.
A force of 10 N displaces a body by 6 m in 3 seconds. The power of the agency applying the force is- a)1.8 W
- b)5 W
- c)180 W
- d)20 W
Correct answer is option 'D'. Can you explain this answer?
A force of 10 N displaces a body by 6 m in 3 seconds. The power of the agency applying the force is
a)
1.8 W
b)
5 W
c)
180 W
d)
20 W
| | Ananya Das answered |
We know, Power :-
= force * displacement/Time
Force is 10 N, displacement = 6 m
Time = 3 s
Then, power = 10*6/3 => 10 * 2 ⇒ 20W
= force * displacement/Time
Force is 10 N, displacement = 6 m
Time = 3 s
Then, power = 10*6/3 => 10 * 2 ⇒ 20W
Which of the following produces energy because of temperature difference at various levels in ocean. - a)Tidal energy
- b)Wave energy
- c)Solar energy
- d)Ocean thermal energy
Correct answer is option 'C'. Can you explain this answer?
Which of the following produces energy because of temperature difference at various levels in ocean.
a)
Tidal energy
b)
Wave energy
c)
Solar energy
d)
Ocean thermal energy
| | Poulomi Nambiar answered |
The correct option is C.
Both will have the same kinetic energy.
Both will have the same kinetic energy.
A body of mass 44 kg is moving at a velocity of 10 m/s is brought to rest in 10mins, the work done is:- a)220 J
- b)22000 J
- c)22 J
- d)-2200J
Correct answer is option 'D'. Can you explain this answer?
A body of mass 44 kg is moving at a velocity of 10 m/s is brought to rest in 10mins, the work done is:
a)
220 J
b)
22000 J
c)
22 J
d)
-2200J
 | Hiral Nambiar answered |
Given:
Mass of the body (m) = 44 kg
Initial velocity (u) = 10 m/s
Final velocity (v) = 0 m/s (body is brought to rest)
Time taken (t) = 10 mins = 10 x 60 = 600 seconds
To find:
Work done (W)
Formula:
The work done on an object is given by the equation:
W = 0.5 * m * (v^2 - u^2)
Calculation:
Substituting the given values into the formula:
W = 0.5 * 44 * (0^2 - 10^2)
= 0.5 * 44 * (-100)
= - 2200 J
Answer:
The work done on the body is -2200 J.
Mass of the body (m) = 44 kg
Initial velocity (u) = 10 m/s
Final velocity (v) = 0 m/s (body is brought to rest)
Time taken (t) = 10 mins = 10 x 60 = 600 seconds
To find:
Work done (W)
Formula:
The work done on an object is given by the equation:
W = 0.5 * m * (v^2 - u^2)
Calculation:
Substituting the given values into the formula:
W = 0.5 * 44 * (0^2 - 10^2)
= 0.5 * 44 * (-100)
= - 2200 J
Answer:
The work done on the body is -2200 J.
According to the law of conservation of energy, which statement is true?- a)Energy can be created and destroyed.
- b)The total energy before and after transformation remains the same.
- c)Energy transformation always leads to a loss of energy.
- d)Only kinetic energy is conserved, not potential energy.
Correct answer is option 'B'. Can you explain this answer?
a)
Energy can be created and destroyed.
b)
The total energy before and after transformation remains the same.
c)
Energy transformation always leads to a loss of energy.
d)
Only kinetic energy is conserved, not potential energy.
 | Let's Tute answered |
The law of conservation of energy states that energy can neither be created nor destroyed, only transformed from one form to another. The total energy in a closed system remains constant before and after any transformation.
Work and Energy:(i) Work done by a force is the product of the force and the displacement in the direction of the force.
(ii) Work has both magnitude and direction.
(iii) An object possessing energy can exert a force on another object.
(iv) The unit of energy is the same as that of work, which is joule (J).
The correct statements are:- a)(i) and (ii)
- b)(iii) and (iv)
- c)(i), (iii) and (iv)
- d)(ii) and (iv)
Correct answer is option 'B'. Can you explain this answer?
(ii) Work has both magnitude and direction.
(iii) An object possessing energy can exert a force on another object.
(iv) The unit of energy is the same as that of work, which is joule (J).
The correct statements are:
a)
(i) and (ii)
b)
(iii) and (iv)
c)
(i), (iii) and (iv)
d)
(ii) and (iv)
 | Nabeel Al-Kaabi answered |
Understanding Work and Energy
In the context of work and energy, let's analyze the statements provided:
Statement (i): Work done by a force is the product of the force and the displacement in the direction of the force.
- This statement is true. Work is defined as the dot product of force and displacement, which means it considers only the component of force that acts in the direction of displacement.
Statement (ii): Work has both magnitude and direction.
- This statement is false. Although work has magnitude (measured in joules), it is a scalar quantity, meaning it does not have a direction associated with it.
Statement (iii): An object possessing energy can exert a force on another object.
- This statement is true. An object with energy (kinetic, potential, etc.) can perform work, thereby exerting a force on another object.
Statement (iv): The unit of energy is the same as that of work, which is joule (J).
- This statement is also true. Both work and energy are measured in joules, making their units identical.
Conclusion
Based on the analysis:
- The correct statements are (i), (iii), and (iv).
- Therefore, option 'C' is correct as it includes statements (i), (iii), and (iv), while statement (ii) is incorrect because work is not a vector quantity.
In summary, understanding the definitions and properties of work and energy is crucial for grasping fundamental physics concepts.
In the context of work and energy, let's analyze the statements provided:
Statement (i): Work done by a force is the product of the force and the displacement in the direction of the force.
- This statement is true. Work is defined as the dot product of force and displacement, which means it considers only the component of force that acts in the direction of displacement.
Statement (ii): Work has both magnitude and direction.
- This statement is false. Although work has magnitude (measured in joules), it is a scalar quantity, meaning it does not have a direction associated with it.
Statement (iii): An object possessing energy can exert a force on another object.
- This statement is true. An object with energy (kinetic, potential, etc.) can perform work, thereby exerting a force on another object.
Statement (iv): The unit of energy is the same as that of work, which is joule (J).
- This statement is also true. Both work and energy are measured in joules, making their units identical.
Conclusion
Based on the analysis:
- The correct statements are (i), (iii), and (iv).
- Therefore, option 'C' is correct as it includes statements (i), (iii), and (iv), while statement (ii) is incorrect because work is not a vector quantity.
In summary, understanding the definitions and properties of work and energy is crucial for grasping fundamental physics concepts.
In the SI system, the unit of potential energy is:- a)Newton
- b)Joule
- c)Watt
- d)Metre per second
Correct answer is option 'B'. Can you explain this answer?
In the SI system, the unit of potential energy is:
a)
Newton
b)
Joule
c)
Watt
d)
Metre per second
| | Swati Verma answered |
Potential energy is energy stored in matter. Joule is the SI unit of energy.
Which of the following is not an example of potential energy?- a)A compressed spring
- b)Water stored in the reservoir of dam
- c)A stretched rubber band
- d)A moving car
Correct answer is option 'D'. Can you explain this answer?
Which of the following is not an example of potential energy?
a)
A compressed spring
b)
Water stored in the reservoir of dam
c)
A stretched rubber band
d)
A moving car
 | Aman Majumdar answered |
A moving car is an example of Kinetic energy whereas water stored in a dam, compressed springs and stretched rubber band are examples of potential energy.
Assertion (A): Work is not done when a force is applied to an object, but there is no displacement of the object.Reason (R): According to the scientific definition of work, work is defined as force multiplied by displacement. If there is no displacement, no work is done.- a)If both Assertion and Reason are true and Reason is the correct explanation of Assertion
- b)If both Assertion and Reason are true but Reason is not the correct explanation of Assertion
- c)If Assertion is true but Reason is false
- d)If both Assertion and Reason are false
Correct answer is option 'A'. Can you explain this answer?
Assertion (A): Work is not done when a force is applied to an object, but there is no displacement of the object.
Reason (R): According to the scientific definition of work, work is defined as force multiplied by displacement. If there is no displacement, no work is done.
a)
If both Assertion and Reason are true and Reason is the correct explanation of Assertion
b)
If both Assertion and Reason are true but Reason is not the correct explanation of Assertion
c)
If Assertion is true but Reason is false
d)
If both Assertion and Reason are false
 | Flembe Academy answered |
- In this scenario, the Assertion is true because work in the scientific sense involves both force and displacement. If there is no displacement, according to the scientific definition, work is not done.
- The Reason is also correct, as it accurately explains why work is not done when there is no displacement.
- Therefore, the correct answer is Option A, where both the Assertion and the Reason are true and the Reason correctly explains the Assertion.
When two identical bodies are in motion, the body with a higher velocity has __________.- a)Lower Kinetic Energy
- b)Higher Kinetic Energy
- c)No Kinetic Energy
- d)None of the options
Correct answer is option 'B'. Can you explain this answer?
When two identical bodies are in motion, the body with a higher velocity has __________.
a)
Lower Kinetic Energy
b)
Higher Kinetic Energy
c)
No Kinetic Energy
d)
None of the options
 | Ritika Kumar answered |
Understanding Kinetic Energy
Kinetic energy is the energy that an object possesses due to its motion. It is directly related to both the mass of the object and the square of its velocity. The formula for kinetic energy (KE) is given by:
KE = 1/2 mv²
Where:
- m = mass of the object
- v = velocity of the object
Key Concepts
- Identical Bodies: In this scenario, both bodies have the same mass (m).
- Higher Velocity: When comparing two identical bodies, the one with the higher velocity (v) will have a greater kinetic energy.
Impact of Velocity on Kinetic Energy
- Square of Velocity: Since kinetic energy is proportional to the square of velocity (v²), even a small increase in velocity leads to a significant increase in kinetic energy.
- Example: If one body is moving at 2 m/s and the other at 4 m/s, the kinetic energy will be:
- For 2 m/s: KE = 1/2 m (2)² = 2m
- For 4 m/s: KE = 1/2 m (4)² = 8m
- Conclusion: The body moving at 4 m/s has 4 times the kinetic energy of the body moving at 2 m/s.
Final Thoughts
Given that the body with a higher velocity has a quadratic relationship with its kinetic energy, it is clear that:
- Correct Answer: The body with a higher velocity has Higher Kinetic Energy.
This illustrates how motion and energy are intricately linked, emphasizing the importance of velocity in determining kinetic energy.
Kinetic energy is the energy that an object possesses due to its motion. It is directly related to both the mass of the object and the square of its velocity. The formula for kinetic energy (KE) is given by:
KE = 1/2 mv²
Where:
- m = mass of the object
- v = velocity of the object
Key Concepts
- Identical Bodies: In this scenario, both bodies have the same mass (m).
- Higher Velocity: When comparing two identical bodies, the one with the higher velocity (v) will have a greater kinetic energy.
Impact of Velocity on Kinetic Energy
- Square of Velocity: Since kinetic energy is proportional to the square of velocity (v²), even a small increase in velocity leads to a significant increase in kinetic energy.
- Example: If one body is moving at 2 m/s and the other at 4 m/s, the kinetic energy will be:
- For 2 m/s: KE = 1/2 m (2)² = 2m
- For 4 m/s: KE = 1/2 m (4)² = 8m
- Conclusion: The body moving at 4 m/s has 4 times the kinetic energy of the body moving at 2 m/s.
Final Thoughts
Given that the body with a higher velocity has a quadratic relationship with its kinetic energy, it is clear that:
- Correct Answer: The body with a higher velocity has Higher Kinetic Energy.
This illustrates how motion and energy are intricately linked, emphasizing the importance of velocity in determining kinetic energy.
Assertion (A): An object thrown at a certain angle to the ground moves in a curved path and falls back to the ground. The initial and the final points of the path of the object lie on the same horizontal line.Reason (R): The work done by the force of gravity on the object in this scenario is zero.- a)If both Assertion and Reason are true and Reason is the correct explanation of Assertion
- b)If both Assertion and Reason are true but Reason is not the correct explanation of Assertion
- c)If Assertion is true but Reason is false
- d)If both Assertion and Reason are false
Correct answer is option 'C'. Can you explain this answer?
Assertion (A): An object thrown at a certain angle to the ground moves in a curved path and falls back to the ground. The initial and the final points of the path of the object lie on the same horizontal line.
Reason (R): The work done by the force of gravity on the object in this scenario is zero.
a)
If both Assertion and Reason are true and Reason is the correct explanation of Assertion
b)
If both Assertion and Reason are true but Reason is not the correct explanation of Assertion
c)
If Assertion is true but Reason is false
d)
If both Assertion and Reason are false
 | Prepworks Coaching answered |
- Assertion's Correctness: The assertion that an object follows a curved path and falls back to the ground with the initial and final points on the same horizontal line is correct for a projectile motion scenario.
- Reason's Correctness: The reason given that the work done by the force of gravity in this situation is zero is incorrect. Gravity does work on the object during its projectile motion, constantly changing its speed and direction.
- Explanation: In projectile motion, gravity constantly acts on the object, causing it to accelerate towards the ground. This acceleration due to gravity affects the object's path, making it follow a curved trajectory. The work done by gravity is not zero, as it continuously affects the object's motion.
- Conclusion: While the assertion is true regarding the path of the object, the reason provided is false since gravity does work on the object during its motion. Therefore, Assertion is true, but Reason is false.
A body is moved through a distance of 3 m in the following different ways. In which case is the maximum work done?- a)when pushed over an inclined plane
- b)when lifted vertically upward
- c)when pushed over smooth rollers
- d)when pushed on a plain horizontal surface
Correct answer is option 'B'. Can you explain this answer?
A body is moved through a distance of 3 m in the following different ways. In which case is the maximum work done?
a)
when pushed over an inclined plane
b)
when lifted vertically upward
c)
when pushed over smooth rollers
d)
when pushed on a plain horizontal surface
| | Ishita Khanna answered |
Work done= Mgg
Work will be maximum when the change in height is Maximum, thus when it is lifted vertically upward.
Choose the correctly matched pair.- a)Work done when force is zero - Positive work
- b)Work done when force and displacement are in opposite directions - Negative work
- c)Work done when force is applied but no displacement occurs - Work is done
- d)Work done when force and displacement are perpendicular - Maximum work
Correct answer is option 'B'. Can you explain this answer?
a)
Work done when force is zero - Positive work
b)
Work done when force and displacement are in opposite directions - Negative work
c)
Work done when force is applied but no displacement occurs - Work is done
d)
Work done when force and displacement are perpendicular - Maximum work
| | Prepworks Coaching answered |
- Let's evaluate each option based on the principles described in the text:
- Option A: (a) Work done when force is zero - Positive workThis is incorrect. When the force applied is zero, no work is done, regardless of any displacement.
- Option B: (b) Work done when force and displacement are in opposite directions - Negative workThis is correct. When the force acts in the opposite direction to the displacement, the work done is negative, as explained in the text.
- Option C: (c) Work done when force is applied but no displacement occurs - Work is doneThis is incorrect. For work to be done according to the scientific definition, there must be both force and displacement. If there's no displacement, no work is done.
- Option D: (d) Work done when force and displacement are perpendicular - Maximum workThis is incorrect. When force and displacement are perpendicular, no work is done because the cosine of 90 degrees is zero, making the work zero.
- Therefore, the correctly matched pair is Option B.
1 J is the energy required to do ____ of work.- a)1 N
- b)98 J
- c)1 N·m
- d)9.8 N
Correct answer is option 'C'. Can you explain this answer?
1 J is the energy required to do ____ of work.
a)
1 N
b)
98 J
c)
1 N·m
d)
9.8 N
 | Imk Pathshala answered |
1 joule (J) is defined as the amount of work done when a force of 1 newton (N) moves an object by 1 metre (m) in the direction of the force. The unit of work (and energy) is the newton-metre, which is also called a joule. Therefore, 1 joule is the energy required to do 1 newton-metre (1 N·m) of work. So, option c) 1 N·m is correct.
Two bodies of masses m and 4 m are moving with equal kinetic energy. The ratio of velocities with which they are traveling is :- a)3:4
- b)1:2
- c)4:5
- d)2:1
Correct answer is option 'D'. Can you explain this answer?
Two bodies of masses m and 4 m are moving with equal kinetic energy. The ratio of velocities with which they are traveling is :
a)
3:4
b)
1:2
c)
4:5
d)
2:1
| | Vikram Kapoor answered |
since kinetic energies are equal
KE1 = KE2
mv12/2 = 4mv22/2
v1/v2 = √4/1 = 2:1
What are the various factors affecting kinetic energy?- a)Mass
- b)Momentum
- c)Velocity
- d)All the above options
Correct answer is option 'D'. Can you explain this answer?
What are the various factors affecting kinetic energy?
a)
Mass
b)
Momentum
c)
Velocity
d)
All the above options
| | Imk Pathshala answered |
Answer: (d) All the above options
Explanation: Factors affecting kinetic energy are mass, momentum, and velocity.
A body of mass 4 kg has a momentum of 25 kg m/s, its K.E. is:- a)70.66 J
- b)78.125 J
- c)100 J
- d)25.5 J
Correct answer is option 'B'. Can you explain this answer?
A body of mass 4 kg has a momentum of 25 kg m/s, its K.E. is:
a)
70.66 J
b)
78.125 J
c)
100 J
d)
25.5 J
 | Samridhi Banerjee answered |
Understanding Momentum and Kinetic Energy
Momentum (p) is defined as the product of mass (m) and velocity (v). It can be expressed as:
Kinetic Energy (K.E.) is given by the formula:
Given:
- Mass (m) = 4 kg
- Momentum (p) = 25 kg m/s
Finding Velocity
To find the velocity (v), we can rearrange the momentum formula:
Calculating Kinetic Energy
Now, substituting the values into the K.E. formula:
Conclusion
Therefore, the Kinetic Energy of the body is:
Thus, the correct answer is option 'B'. This calculation demonstrates the relationship between momentum and kinetic energy using the mass and velocity derived from momentum.
Momentum (p) is defined as the product of mass (m) and velocity (v). It can be expressed as:
p = m × v
Kinetic Energy (K.E.) is given by the formula:
K.E. = 0.5 × m × v²
Given:
- Mass (m) = 4 kg
- Momentum (p) = 25 kg m/s
Finding Velocity
To find the velocity (v), we can rearrange the momentum formula:
v = p / m = 25 kg m/s / 4 kg = 6.25 m/s
Calculating Kinetic Energy
Now, substituting the values into the K.E. formula:
K.E. = 0.5 × m × v²
K.E. = 0.5 × 4 kg × (6.25 m/s)²
K.E. = 0.5 × 4 kg × 39.0625 m²/s²
K.E. = 2 kg × 39.0625 m²/s² = 78.125 J
Conclusion
Therefore, the Kinetic Energy of the body is:
78.125 J
Thus, the correct answer is option 'B'. This calculation demonstrates the relationship between momentum and kinetic energy using the mass and velocity derived from momentum.
The kinetic energy of a body changes from 12 J to 60 J due to the action of a force of 5N on an object of mass 4 kg. The work done by the force is:- a)36 J
- b)60 J
- c)48 J
- d)24 J
Correct answer is option 'C'. Can you explain this answer?
The kinetic energy of a body changes from 12 J to 60 J due to the action of a force of 5N on an object of mass 4 kg. The work done by the force is:
a)
36 J
b)
60 J
c)
48 J
d)
24 J
| | Let's Tute answered |
Change in KE is workdone by work energy theoream 60-12 = 48J
Choose the correctly matched pair:- a)Power - Rate of doing work
- b)Kinetic Energy - Potential energy of a raised object
- c)Mechanical Energy - Only potential energy
- d)Work - Force divided by distance
Correct answer is option 'A'. Can you explain this answer?
a)
Power - Rate of doing work
b)
Kinetic Energy - Potential energy of a raised object
c)
Mechanical Energy - Only potential energy
d)
Work - Force divided by distance
| | Prepworks Coaching answered |
- Option A: Power - Rate of doing work
- This is the correct match. Power is defined as the rate at which work is done. The SI unit of power is watt (W), where 1 W = 1 J/s.
- Option B: Kinetic Energy - Potential energy of a raised object
- This is incorrectly matched. Kinetic energy is the energy possessed by an object due to its motion, not its position. Potential energy is the energy possessed by an object due to its position or height.
- Option C: Mechanical Energy - Only potential energy
- This is incorrect. Mechanical energy is the sum of kinetic and potential energy of an object, not just potential energy.
- Option D: Work - Force divided by distance
- This is incorrect. Work is defined as the force applied on an object multiplied by the distance moved by the object in the direction of the force, not divided by distance.
A mass ‘m’ falls from a height ‘h’ any point on its path the total energy is- a)
- b)mgh/4
- c)mgh
- d)Depends on the height
Correct answer is option 'C'. Can you explain this answer?
A mass ‘m’ falls from a height ‘h’ any point on its path the total energy is
a)
b)
mgh/4
c)
mgh
d)
Depends on the height
| | Ramya patel answered |
according to law of conservation of energy.
A body is acted upon by a force of 25 N and acquires an acceleration of 5 m/s-2. It covers a distance in 2 seconds. If the body starts from rest, what is the kinetic energy acquired by it?- a)75 J
- b)25 J
- c)250 J
- d)100 J
Correct answer is option 'C'. Can you explain this answer?
A body is acted upon by a force of 25 N and acquires an acceleration of 5 m/s-2. It covers a distance in 2 seconds. If the body starts from rest, what is the kinetic energy acquired by it?
a)
75 J
b)
25 J
c)
250 J
d)
100 J
| | Imk Pathshala answered |
First, we determine the mass of the body using F = ma:
25 N = m × 5 m/s² → m = 5 kg.
25 N = m × 5 m/s² → m = 5 kg.
Since the body starts from rest and accelerates at 5 m/s² for 2 seconds, its final velocity is:
v = u + at = 0 + (5)(2) = 10 m/s.
v = u + at = 0 + (5)(2) = 10 m/s.
Hence, the kinetic energy acquired is:
K = 1/2 mv² = 1/2 × 5 × (10)² = 250 J.
K = 1/2 mv² = 1/2 × 5 × (10)² = 250 J.
Thus, the correct answer is 250 J.
The formula to find the work done is- a)W = F + s
- b)W = F x s
- c)W = F - s
- d)W = F/s
Correct answer is option 'B'. Can you explain this answer?
The formula to find the work done is
a)
W = F + s
b)
W = F x s
c)
W = F - s
d)
W = F/s
| | Let's Tute answered |
Answer: (b) W = F.s
Work Done: The work done by a force is calculated as the product of the force and the displacement in the direction of the force.
For an object to have gravitational potential energy only, it must be- a)Accelerating
- b)Moving
- c)Falling
- d)At an elevated position with respect to the ground
Correct answer is option 'D'. Can you explain this answer?
For an object to have gravitational potential energy only, it must be
a)
Accelerating
b)
Moving
c)
Falling
d)
At an elevated position with respect to the ground
| | Prasad Ghoshal answered |
The correct option is D.
An object possesses gravitational potential energy if it is positioned at a height above (or below) the zero height. An object possesses elastic potential energy if it is at a position on an elastic medium other than the equilibrium position.
An object possesses gravitational potential energy if it is positioned at a height above (or below) the zero height. An object possesses elastic potential energy if it is at a position on an elastic medium other than the equilibrium position.
Objects in motion possess energy and can do work; this energy is called_______________. - a)Solar energy
- b)Thermal energy
- c)Potential energy
- d)Kinetic Energy
Correct answer is option 'D'. Can you explain this answer?
Objects in motion possess energy and can do work; this energy is called_______________.
a)
Solar energy
b)
Thermal energy
c)
Potential energy
d)
Kinetic Energy
 | EduRev Class 9 answered |
Answer: (d) Kinetic Energy
Explanation: Kinetic energy is defined as the work needed to accelerate a body of a given mass from rest.
In the case of negative work, the angle between the force and displacement is:- a)0°
- b)45°
- c)90°
- d)180°
Correct answer is option 'D'. Can you explain this answer?
In the case of negative work, the angle between the force and displacement is:
a)
0°
b)
45°
c)
90°
d)
180°
| | Swati Verma answered |
- Work done by any force is the product of the component of the force in the direction of displacement and the magnitude of displacement.
W = F.d = Fd cosθ - When W=−ve, it means cosθ = −ve
Therefore, θ=180º
If the speed of an object doubles, its kinetic energy becomes- a)half
- b)four times
- c)one-fourth
- d)double
Correct answer is option 'B'. Can you explain this answer?
If the speed of an object doubles, its kinetic energy becomes
a)
half
b)
four times
c)
one-fourth
d)
double
| | Mihir Chatterjee answered |
Doubling the speed of an object has a significant effect on its kinetic energy. The relationship between speed and kinetic energy is directly proportional, meaning that as the speed of an object increases, its kinetic energy also increases.
Understanding Kinetic Energy:
Before discussing the effect of doubling the speed on kinetic energy, it is important to understand what kinetic energy is. Kinetic energy is the energy possessed by an object due to its motion. It is dependent on two factors: the mass of the object and its velocity (speed). The formula for calculating kinetic energy is:
Kinetic Energy = (1/2) * mass * velocity^2
Where:
- Kinetic Energy is measured in joules (J)
- Mass is measured in kilograms (kg)
- Velocity (speed) is measured in meters per second (m/s)
Effect of Doubling Speed:
When the speed of an object doubles, it means that the new speed is twice the original speed. Let's consider the initial speed as v and the final speed as 2v (twice the original speed).
Using the formula for kinetic energy, we can calculate the initial kinetic energy (KE1) and the final kinetic energy (KE2) as follows:
KE1 = (1/2) * mass * v^2
KE2 = (1/2) * mass * (2v)^2
Simplifying the equations:
KE1 = (1/2) * mass * v^2
KE2 = (1/2) * mass * 4v^2
We can see that the final kinetic energy (KE2) is four times the initial kinetic energy (KE1). In other words, doubling the speed of an object results in a four-fold increase in its kinetic energy.
Conclusion:
When the speed of an object doubles, its kinetic energy becomes four times greater than its initial kinetic energy. This is because kinetic energy is directly proportional to the square of the velocity. Thus, increasing the velocity by a factor of two results in an increase in kinetic energy by a factor of four.
Understanding Kinetic Energy:
Before discussing the effect of doubling the speed on kinetic energy, it is important to understand what kinetic energy is. Kinetic energy is the energy possessed by an object due to its motion. It is dependent on two factors: the mass of the object and its velocity (speed). The formula for calculating kinetic energy is:
Kinetic Energy = (1/2) * mass * velocity^2
Where:
- Kinetic Energy is measured in joules (J)
- Mass is measured in kilograms (kg)
- Velocity (speed) is measured in meters per second (m/s)
Effect of Doubling Speed:
When the speed of an object doubles, it means that the new speed is twice the original speed. Let's consider the initial speed as v and the final speed as 2v (twice the original speed).
Using the formula for kinetic energy, we can calculate the initial kinetic energy (KE1) and the final kinetic energy (KE2) as follows:
KE1 = (1/2) * mass * v^2
KE2 = (1/2) * mass * (2v)^2
Simplifying the equations:
KE1 = (1/2) * mass * v^2
KE2 = (1/2) * mass * 4v^2
We can see that the final kinetic energy (KE2) is four times the initial kinetic energy (KE1). In other words, doubling the speed of an object results in a four-fold increase in its kinetic energy.
Conclusion:
When the speed of an object doubles, its kinetic energy becomes four times greater than its initial kinetic energy. This is because kinetic energy is directly proportional to the square of the velocity. Thus, increasing the velocity by a factor of two results in an increase in kinetic energy by a factor of four.
Elastic potential energy of a body can be achieved by- a)setting it into motion
- b)raising the body to a height
- c)using an elastic band to tie the body
- d)compressing or stretching the body
Correct answer is option 'D'. Can you explain this answer?
Elastic potential energy of a body can be achieved by
a)
setting it into motion
b)
raising the body to a height
c)
using an elastic band to tie the body
d)
compressing or stretching the body
 | Anirudh Choudhury answered |
Elastic potential energy is the energy stored in an elastic object when it is either compressed or stretched. This type of energy is a result of the object's ability to return to its original shape after being deformed. Elastic potential energy can be achieved by compressing or stretching the body, which is why the correct answer is option 'D'.
Here's a detailed explanation of why compressing or stretching the body can result in elastic potential energy:
1. Definition of elastic potential energy:
- Elastic potential energy is a form of potential energy stored in elastic materials, such as springs or rubber bands.
- It arises from the deformation of the material, and the energy is stored when the material is compressed or stretched.
2. How compression leads to elastic potential energy:
- When a body is compressed, its particles are pushed closer together, causing the object to deform and store potential energy.
- For example, consider a spring. When a force is applied to compress the spring, it resists the compression and stores potential energy.
- The potential energy is directly proportional to the amount of compression. The more the spring is compressed, the more potential energy it stores.
3. How stretching leads to elastic potential energy:
- When a body is stretched, its particles are pulled farther apart, causing the object to deform and store potential energy.
- For instance, imagine a rubber band. When it is stretched, it resists the stretching and stores potential energy.
- The potential energy is directly proportional to the amount of stretch. The more the rubber band is stretched, the more potential energy it stores.
4. Elastic potential energy and Hooke's Law:
- Hooke's Law states that the force needed to compress or stretch an elastic object is directly proportional to the amount of deformation.
- Mathematically, this can be expressed as F = kx, where F is the force applied, k is the spring constant, and x is the displacement from the equilibrium position.
- The potential energy stored in the object is given by the equation PE = (1/2)kx^2, where PE is the elastic potential energy.
- This equation shows that the potential energy is directly proportional to the square of the displacement.
In conclusion, compressing or stretching a body allows it to store elastic potential energy. This energy is stored in the object's deformed state and can be released when the object returns to its original shape.
Here's a detailed explanation of why compressing or stretching the body can result in elastic potential energy:
1. Definition of elastic potential energy:
- Elastic potential energy is a form of potential energy stored in elastic materials, such as springs or rubber bands.
- It arises from the deformation of the material, and the energy is stored when the material is compressed or stretched.
2. How compression leads to elastic potential energy:
- When a body is compressed, its particles are pushed closer together, causing the object to deform and store potential energy.
- For example, consider a spring. When a force is applied to compress the spring, it resists the compression and stores potential energy.
- The potential energy is directly proportional to the amount of compression. The more the spring is compressed, the more potential energy it stores.
3. How stretching leads to elastic potential energy:
- When a body is stretched, its particles are pulled farther apart, causing the object to deform and store potential energy.
- For instance, imagine a rubber band. When it is stretched, it resists the stretching and stores potential energy.
- The potential energy is directly proportional to the amount of stretch. The more the rubber band is stretched, the more potential energy it stores.
4. Elastic potential energy and Hooke's Law:
- Hooke's Law states that the force needed to compress or stretch an elastic object is directly proportional to the amount of deformation.
- Mathematically, this can be expressed as F = kx, where F is the force applied, k is the spring constant, and x is the displacement from the equilibrium position.
- The potential energy stored in the object is given by the equation PE = (1/2)kx^2, where PE is the elastic potential energy.
- This equation shows that the potential energy is directly proportional to the square of the displacement.
In conclusion, compressing or stretching a body allows it to store elastic potential energy. This energy is stored in the object's deformed state and can be released when the object returns to its original shape.
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