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Work & Energy - Olympiad Level MCQ, Class 9 Science - Class 9 MCQ


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25 Questions MCQ Test - Work & Energy - Olympiad Level MCQ, Class 9 Science

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Work & Energy - Olympiad Level MCQ, Class 9 Science - Question 1

No work is done when an object moves:

Detailed Solution for Work & Energy - Olympiad Level MCQ, Class 9 Science - Question 1

Work is not said to be done when an object moves at 90 degree to the direction of the force. Because work done = F.x Cosθ = F.x Cos90 = 0 (Since Cos90 degree is zero). Hence when force and displacement angle are perpendicular to each other no work is said to be done.

Work & Energy - Olympiad Level MCQ, Class 9 Science - Question 2

Capacity of doing work is called:

Detailed Solution for Work & Energy - Olympiad Level MCQ, Class 9 Science - Question 2
Capacity of doing work is called energy.
The concept of capacity of doing work is known as energy. Energy is the ability or capacity to do work or produce a change. It is a fundamental concept in physics and is present in various forms in the universe. Here's a detailed explanation of why energy is the correct answer:
Definition of Energy:
- Energy is a scalar physical quantity that is associated with objects and systems and is capable of being transferred or converted to different forms.
- It is measured in units such as joules (J) or calories (cal).
Characteristics of Energy:
- Energy exists in different forms, such as kinetic energy, potential energy, thermal energy, electrical energy, etc.
- Energy can be converted from one form to another, but it cannot be created or destroyed according to the law of conservation of energy.
Relation to Work:
- Work is defined as the transfer of energy from one object to another through the application of force along the direction of displacement.
- Therefore, work and energy are closely related concepts and can be considered interchangeable in many situations.
Examples:
- When a person lifts a heavy object, the person is doing work by transferring energy to the object to increase its potential energy.
- When a car accelerates, the engine converts chemical energy from the fuel into kinetic energy, allowing the car to move.
- When an electric current flows through a light bulb, electrical energy is converted into light energy and thermal energy.
In conclusion, the capacity of doing work is called energy. It is a fundamental concept in physics and is present in various forms in the universe.
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Work & Energy - Olympiad Level MCQ, Class 9 Science - Question 3

Energy possessed by a body on account of position or configuration is called

Detailed Solution for Work & Energy - Olympiad Level MCQ, Class 9 Science - Question 3
Explanation:
Potential energy is the energy possessed by a body due to its position or configuration. It is stored energy that has the potential to be converted into other forms of energy.
To understand potential energy better, let's break it down into key points:
1. Definition: Potential energy is the energy stored in an object based on its position or configuration relative to other objects.
2. Types of potential energy: There are different types of potential energy, including gravitational potential energy, elastic potential energy, chemical potential energy, and electrical potential energy.
3. Gravitational potential energy: It is the potential energy stored in an object due to its height above the ground. The higher the object is, the greater its gravitational potential energy.
4. Elastic potential energy: It is the potential energy stored in elastic materials, such as a stretched rubber band or a compressed spring. The more the material is stretched or compressed, the greater its elastic potential energy.
5. Chemical potential energy: It is the potential energy stored in chemical bonds. When chemical reactions occur, this energy can be released or absorbed.
6. Electrical potential energy: It is the potential energy stored in electric fields due to the separation of charges. The closer the charges are, the greater their electrical potential energy.
In conclusion, potential energy is the energy that a body possesses based on its position or configuration. It can be converted into other forms of energy, such as kinetic energy, when the body moves or its configuration changes.
Work & Energy - Olympiad Level MCQ, Class 9 Science - Question 4

Energy possessed by a body on account of its motion is called:

Detailed Solution for Work & Energy - Olympiad Level MCQ, Class 9 Science - Question 4
Definition of Kinetic Energy:
- Kinetic energy is the energy possessed by a body on account of its motion.
- It is a form of energy that an object possesses due to its motion.
Explanation of the Options:
A. Mechanical Energy:
- Mechanical energy is the sum of potential energy and kinetic energy.
- It includes both the energy of motion (kinetic energy) and the energy stored in an object's position (potential energy).
- While kinetic energy is a component of mechanical energy, it is not the only form of mechanical energy.
B. Potential Energy:
- Potential energy is the energy that an object possesses due to its position or state.
- It is stored energy that can be converted into other forms of energy, such as kinetic energy.
- While potential energy can be converted into kinetic energy, it is not specifically related to the energy possessed by a body in motion.
C. Kinetic Energy:
- Kinetic energy is the energy possessed by a body on account of its motion.
- It is directly related to the mass and velocity of an object.
- The formula for calculating kinetic energy is KE = 1/2 mv^2, where KE represents kinetic energy, m represents mass, and v represents velocity.
D. Magnetic Energy:
- Magnetic energy refers to the potential energy stored in a magnetic field.
- It is related to the ability of a magnetic field to do work or exert a force on other magnetic objects.
- Magnetic energy is not directly related to the motion of a body and is not the correct answer in this case.
Conclusion:
Based on the given options and the definition of kinetic energy, the correct answer is C: Kinetic energy. Kinetic energy is the energy possessed by a body on account of its motion, while the other options are either different forms of energy or not directly related to the motion of a body.
Work & Energy - Olympiad Level MCQ, Class 9 Science - Question 5

A stone rolls down an inclined plane. Midway during the motion, the stone has:

Detailed Solution for Work & Energy - Olympiad Level MCQ, Class 9 Science - Question 5

The stone rolling down an inclined plane experiences both kinetic and potential energy. Here's a detailed explanation:
1. Initial state:
- At the starting point of the motion, the stone is stationary and at a higher position on the inclined plane.
- It possesses potential energy due to its position relative to the ground.
2. During motion:
- As the stone rolls down the inclined plane, it gains speed and accelerates.
- The stone's potential energy decreases as it moves closer to the ground.
- At the midpoint of the motion, the stone has converted some of its potential energy into kinetic energy.
3. Kinetic energy:
- Kinetic energy is the energy possessed by an object due to its motion.
- As the stone moves down the inclined plane, it gains speed and thus has kinetic energy.
- The amount of kinetic energy depends on the mass of the stone and its velocity.
4. Potential energy:
- Potential energy is the energy possessed by an object due to its position or height above the ground.
- At the midpoint of the motion, the stone still has some potential energy, although it is lower than its initial potential energy.
- The amount of potential energy depends on the mass of the stone, acceleration due to gravity, and the height of the inclined plane.
5. Conservation of energy:
- The total mechanical energy of the stone, which is the sum of its kinetic and potential energy, remains constant throughout the motion.
- As the stone gains kinetic energy, its potential energy decreases, but the total energy remains the same.
Therefore, at the midpoint of the motion, the stone possesses both kinetic and potential energy. The correct answer is option C: both kinetic and potential energy.
Work & Energy - Olympiad Level MCQ, Class 9 Science - Question 6

An aeroplane flying at a height of 20,000 m at a speed of 300 kmh-1 has:

Detailed Solution for Work & Energy - Olympiad Level MCQ, Class 9 Science - Question 6

To determine whether the aeroplane has only potential energy, only kinetic energy, both potential and kinetic energy, or none of the above, we need to consider the definitions of potential and kinetic energy.
Potential Energy:
Potential energy is the energy possessed by an object due to its position or state. It is the energy that can be converted into other forms of energy when the object is in motion or undergoes a change.
Kinetic Energy:
Kinetic energy is the energy possessed by an object due to its motion. It depends on the mass and velocity of the object and is the energy associated with the object's movement.
Now let's analyze the given scenario:
Height of the Aeroplane:
The aeroplane is flying at a height of 20,000 m. This height indicates a potential energy because the aeroplane has the potential to do work or convert this energy into other forms (such as kinetic energy).
Speed of the Aeroplane:
The aeroplane is flying at a speed of 300 km/h. This speed indicates kinetic energy because the aeroplane is in motion.
Based on the above analysis, we can conclude that the aeroplane has both potential and kinetic energy. Therefore, the correct answer is option C: both potential and kinetic energy.
In summary:
The aeroplane flying at a height of 20,000 m at a speed of 300 km/h has both potential and kinetic energy. The potential energy is due to its height, and the kinetic energy is due to its motion.
Work & Energy - Olympiad Level MCQ, Class 9 Science - Question 7

A stone is placed on the top of a building of height 'h'. Its potential energy is directly proportional to its:

Detailed Solution for Work & Energy - Olympiad Level MCQ, Class 9 Science - Question 7
Explanation:
The potential energy of an object is the energy that it possesses due to its position relative to other objects. In the case of a stone placed on the top of a building, its potential energy is directly proportional to its height above the ground.
Factors affecting potential energy:
1. Mass: The potential energy is directly proportional to the mass of the stone. A heavier stone will have more potential energy than a lighter stone.
2. Height: The potential energy is directly proportional to the height of the stone above the ground. The higher the stone is placed, the more potential energy it will have.
3. Acceleration due to gravity: The potential energy is also directly proportional to the acceleration due to gravity. The higher the value of gravity, the more potential energy the stone will have.
Conclusion:
Therefore, the potential energy of a stone placed on the top of a building is directly proportional to its mass, height, and acceleration due to gravity. Hence, the correct answer is option D: all the above.
Work & Energy - Olympiad Level MCQ, Class 9 Science - Question 8

If a body is raised through height 'h' on the surface of earth and the energy spent is E, then for the same amount

of energy the body on the surface of moon will rise through the height of:

Detailed Solution for Work & Energy - Olympiad Level MCQ, Class 9 Science - Question 8
we know that potential energy = mgh 
here P.E=E E=mgh 
we know that that acceleration due to gravity on moon is 1/6th ofacceleration due to gravity on earth so g/6E=mg/6h*6body wiil rise to 6h.
Work & Energy - Olympiad Level MCQ, Class 9 Science - Question 9

The kinetic energy of a body is directly proportional to its:

Detailed Solution for Work & Energy - Olympiad Level MCQ, Class 9 Science - Question 9
Explanation:

The kinetic energy of a body is given by the equation:


Kinetic Energy (KE) = 1/2 * mass * (velocity)^2


Breakdown of the equation:



  • Mass: The mass of an object is a measure of its inertia, or the amount of matter it contains. It represents the quantity of matter in an object.

  • Velocity: Velocity is a measure of how fast an object is moving in a specific direction. It is a vector quantity that includes both speed and direction.

  • (Velocity)^2: The square of the velocity is used in the equation to account for the fact that kinetic energy is proportional to the square of the velocity.


Relationship between kinetic energy and its factors:



  • Mass: The kinetic energy of a body is directly proportional to its mass. This means that as the mass of an object increases, its kinetic energy also increases, assuming the velocity remains constant.

  • Velocity: The kinetic energy of a body is directly proportional to the square of its velocity. This means that as the velocity of an object increases, its kinetic energy increases at a faster rate.


Conclusion:


Based on the equation and the relationship between kinetic energy and its factors, we can conclude that the kinetic energy of a body is directly proportional to both its mass and the square of its velocity. Therefore, the correct answer is D: both (A) and (C).

Work & Energy - Olympiad Level MCQ, Class 9 Science - Question 10

A ball is thrown upward from a point P, reaches to the highest point Q :

Detailed Solution for Work & Energy - Olympiad Level MCQ, Class 9 Science - Question 10

To analyze the situation, let's consider the different forms of energy at points P and Q.
At point P:
- The ball is thrown upward, so it has a certain initial velocity.
- Therefore, the ball has kinetic energy at point P.
At point Q:
- The ball reaches the highest point in its trajectory.
- At the highest point, the ball momentarily comes to a stop before falling back down.
- Since the ball is momentarily at rest, its velocity and therefore its kinetic energy at point Q is zero.
- However, the ball is at the highest point of its trajectory, so it has the maximum potential energy.
Therefore, we can conclude that:
- The kinetic energy at point P is not equal to the kinetic energy at point Q.
- The potential energy at point P is not equal to the potential energy at point Q.
- The potential energy at point P is equal to the kinetic energy at point Q. (Option C)
Thus, the correct answer is C: kinetic energy at P is equal to potential energy at Q.
Work & Energy - Olympiad Level MCQ, Class 9 Science - Question 11

The spring will have maximum potential energy when        

Detailed Solution for Work & Energy - Olympiad Level MCQ, Class 9 Science - Question 11
Yes because when it is pulled out and compressed then the spring rise to a height which is maximum at that point.So it will have maximum potential energy.
Work & Energy - Olympiad Level MCQ, Class 9 Science - Question 12

When the speed of a particle is increased 3 times, its kinetic energy:

Detailed Solution for Work & Energy - Olympiad Level MCQ, Class 9 Science - Question 12

The kinetic energy of a particle is given by the formula:
K.E. = (1/2)mv^2
where m is the mass of the particle and v is its velocity.
To determine how the kinetic energy changes when the speed of the particle is increased 3 times, we can compare the initial kinetic energy (K.E.1) with the final kinetic energy (K.E.2).
Let's assume the initial speed of the particle is v1 and the final speed is v2.
So, v2 = 3v1 (since the speed is increased 3 times).
Now, let's compare the initial and final kinetic energies using the formula above:
K.E.1 = (1/2)mv1^2
K.E.2 = (1/2)mv2^2
To compare the two kinetic energies, we can take the ratio of K.E.2 to K.E.1:
K.E.2/K.E.1 = [(1/2)m(3v1)^2] / [(1/2)mv1^2]
= (9/2)(m v1^2) / (1/2)(m v1^2)
= 9
Therefore, the final kinetic energy (K.E.2) is 9 times the initial kinetic energy (K.E.1).
So, the correct answer is option C: increases 9 times.
Work & Energy - Olympiad Level MCQ, Class 9 Science - Question 13

A force of 7N acts on an object through a distance of 8m in its own direction. The work done is :

Detailed Solution for Work & Energy - Olympiad Level MCQ, Class 9 Science - Question 13

To calculate the work done, we can use the formula:
Work Done = Force x Distance
Given:
Force = 7N
Distance = 8m
Using the formula, we can substitute the values:
Work Done = 7N x 8m
Calculating the multiplication:
Work Done = 56N·m
Since the unit of work is Joule (J), we need to convert N·m to J:
1 N·m = 1 J
Therefore:
Work Done = 56N·m = 56J
Hence, the work done is 56J. Therefore, the correct answer is option C.
Work & Energy - Olympiad Level MCQ, Class 9 Science - Question 14

A pair of bullocks exerts a force of 140N on a plough. The field being ploughed is 15m long. How much work is done in ploughing the length of the field?

Detailed Solution for Work & Energy - Olympiad Level MCQ, Class 9 Science - Question 14
Given:
- Force exerted by the pair of bullocks = 140N
- Length of the field = 15m
To find:
- The amount of work done in ploughing the length of the field
Formula:
- Work (W) = Force (F) × Distance (D)

- Substitute the given values into the formula:
- W = 140N × 15m
- Calculate the product:
- W = 2100N·m or 2100J
Answer:
- The amount of work done in ploughing the length of the field is 2100J. Therefore, option C is correct.
Work & Energy - Olympiad Level MCQ, Class 9 Science - Question 15

The kinetic energy of an object of mass 'm', moving with a velocity of 5 ms-1 is 25 J. If the velocity is increased

by three times, the kinetic energy is :

Detailed Solution for Work & Energy - Olympiad Level MCQ, Class 9 Science - Question 15

To find the new kinetic energy when the velocity is increased by three times, we need to use the equation for kinetic energy:
Kinetic Energy (KE) = 1/2 * mass * velocity^2
Given information:
Mass (m) = m
Initial velocity (v1) = 5 m/s
Initial kinetic energy (KE1) = 25 J
We need to find:
New kinetic energy (KE2) when the velocity is increased by three times.
Let's calculate the initial kinetic energy (KE1) using the given data:
KE1 = 1/2 * m * v1^2
= 1/2 * m * (5 m/s)^2
= 1/2 * m * 25 m^2/s^2
= 12.5 m^2/s^2
Now, let's calculate the new kinetic energy (KE2) when the velocity is increased by three times (v2 = 3 * v1):
KE2 = 1/2 * m * v2^2
= 1/2 * m * (3 * v1)^2
= 1/2 * m * 9 * v1^2
= 4.5 * m * v1^2
= 4.5 * 25 J
= 112.5 J
Therefore, when the velocity is increased by three times, the new kinetic energy (KE2) is 112.5 J.
Answer: B. 225J
Work & Energy - Olympiad Level MCQ, Class 9 Science - Question 16

An electric lamp consumes 1000 J of electric energy in 10 second. The power of lamp is :

Detailed Solution for Work & Energy - Olympiad Level MCQ, Class 9 Science - Question 16

To calculate the power of the lamp, we can use the formula:
Power (P) = Energy (E) / Time (t)
Given:
Energy (E) = 1000 J
Time (t) = 10 s
Substituting the values into the formula, we get:
P = 1000 J / 10 s
Simplifying the equation, we find:
P = 100 W
Therefore, the power of the lamp is 100 W.
Answer: C. 100 W
Work & Energy - Olympiad Level MCQ, Class 9 Science - Question 17

A body of mass 20 kg, slows down from 5 ms-1 to 2 ms-1 by a retarding force. The work done by the force is:

Detailed Solution for Work & Energy - Olympiad Level MCQ, Class 9 Science - Question 17

Given:
Mass of the body (m) = 20 kg
Initial velocity (u) = 5 m/s
Final velocity (v) = 2 m/s
We need to find the work done (W) by the retarding force.
The work done by a force can be calculated using the equation:
W = (1/2) * m * (v^2 - u^2)
Calculating the values:
W = (1/2) * 20 * (2^2 - 5^2)
W = (1/2) * 20 * (4 - 25)
W = (1/2) * 20 * (-21)
W = 10 * (-21)
W = -210 J
Therefore, the work done by the retarding force is -210 J.
Answer: D. -210J
Work & Energy - Olympiad Level MCQ, Class 9 Science - Question 18

A mass of 10 kg at point A on a table is moved to point B. If the line joining the A and B is horizontal, the

work done by the body is : [a = 10 ms-2]

Detailed Solution for Work & Energy - Olympiad Level MCQ, Class 9 Science - Question 18
Work done = Force × Displacement Force = mass × acceleration so, work done = mass × acceleration × Displacement W = 10 × 10 × AB = 100N × AB
Work & Energy - Olympiad Level MCQ, Class 9 Science - Question 19

A certain household consumes 250 units of electric energy in a House. The energy consumed in mega joule is:

Detailed Solution for Work & Energy - Olympiad Level MCQ, Class 9 Science - Question 19
1 unit=1 kwh
= 3.6×10^6 j

then,
250unit=250×3.6×10^6= 900×10^6

10^6joule = 1mega joule
so,
900×10^6joule =900MJ(Ans).
Work & Energy - Olympiad Level MCQ, Class 9 Science - Question 20

An object of mass 40 kg (g = 10 ms-2) is raised to a height of 8 m above the ground. The gain potential

energy by the object:

Detailed Solution for Work & Energy - Olympiad Level MCQ, Class 9 Science - Question 20
Since potential energy is mgh. so
40kg × 10m/s2 × 8m=3200J
Work & Energy - Olympiad Level MCQ, Class 9 Science - Question 21

An electric heater is rated 1500 W. The energy used by it in 10 hours is :

Detailed Solution for Work & Energy - Olympiad Level MCQ, Class 9 Science - Question 21
150 kWh= 15000 kilowatt per hour=1500 W*10 hours=15000 kilowatt per hour
Work & Energy - Olympiad Level MCQ, Class 9 Science - Question 22

An object of mass m is moving with a constant velocity 'u'. The work done on the object to bring it to rest is :

Detailed Solution for Work & Energy - Olympiad Level MCQ, Class 9 Science - Question 22

To bring the object to rest, we need to apply a force in the opposite direction of its motion. This force will act against the object's velocity and eventually bring it to rest.
The work done on an object is given by the equation:
Work = Force x Distance
In this case, the force required to bring the object to rest is equal to the force of friction, which is given by the equation:
Force = Mass x Acceleration
Since the object is moving with a constant velocity, its acceleration is zero. Therefore, the force required to bring the object to rest is also zero.
As a result, the work done on the object to bring it to rest is zero. Therefore, none of the options provided (A, B, C, or D) are correct.
Correct Answer: None of the options provided.
Work & Energy - Olympiad Level MCQ, Class 9 Science - Question 23

A car of mass 1500 kg is moving with a velocity of 60 kmh-2. The work done by its brakes to bring it to rest is:

Detailed Solution for Work & Energy - Olympiad Level MCQ, Class 9 Science - Question 23
The
Given:
- Mass of the car (m) = 1500 kg
- Velocity of the car (v) = 60 km/h = 60,000 m/3600 s = 16.67 m/s
To find:
- The work done by the brakes to bring the car to rest.
Formula:
- The work done (W) is given by the formula: W = 1/2 * m * v^2
Substituting the given values into the formula:
W = 1/2 * 1500 kg * (16.67 m/s)^2
W = 1/2 * 1500 kg * 277.89 m^2/s^2
W = 208,417.5 J
Converting Joules to kilojoules:
W = 208,417.5 J * (1 kJ / 1000 J)
W = 208.42 kJ
Therefore, the work done by the brakes to bring the car to rest is 208.42 kJ.
Answer: A. 208.42 kJ
Work & Energy - Olympiad Level MCQ, Class 9 Science - Question 24

The energy consumed (in kWh) by four devices of 500W each in 10 hours is :

Detailed Solution for Work & Energy - Olympiad Level MCQ, Class 9 Science - Question 24
Each device consumes 500 Wh in 1 hour.
So, in 10 hours 1 device will consume 500 * 10 = 5000 Wh
Since there are 4 identical devices, the total energy consumed = 5000 * 4 = 20,000 Wh
20,000 Wh = 20 kWh.
Work & Energy - Olympiad Level MCQ, Class 9 Science - Question 25

A locomotive exerts a force of 7500N and pulls a train by 1.5 km. The work done by the locomotive in mega joules is

Detailed Solution for Work & Energy - Olympiad Level MCQ, Class 9 Science - Question 25

 

Force = 7500N
Displacement = 1.5 km = 1.5 × 1000 m
Work done = force × displacement
= 7500 × 1.5 × 1000 joule
= 7500 × 1500 joule
= 11250000 joule
= 11.25 Mega jould

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