Work And Energy, Science, Class 9 - Test - Class 9 MCQ

Unit of Work: Joule

• Physical Quantity: Energy

The unit of work, joule, is also the unit of energy. Energy can be defined as the capacity to do work or the ability to cause change. Therefore, work and energy are closely related and have the same unit of measure.

Other Physical Quantities:

• Power: Power is the rate at which work is done or energy is transferred. It is measured in joules per second, also known as watts. Therefore, power is not the physical quantity that has the same unit as work.


• Velocity: Velocity is a measure of the rate at which an object changes its position. It is measured in meters per second. Therefore, velocity does not have the same unit as work.


• Force: Force is a push or pull that can cause an object to accelerate. It is measured in newtons. Therefore, force does not have the same unit as work.

Therefore, the correct answer is C: Energy. Energy is the physical quantity that has the same unit as work, which is joule.

Introduction:
Potential energy is the energy stored in an object due to its position or configuration. In the case of a spring, its potential energy depends on how it is manipulated.
Explanation:
The potential energy of a spring can be determined by considering its elongation or compression.
When the spring is pulled out:
- When a spring is pulled out or stretched, it is elongated.
- Elongating the spring requires work, which is stored as potential energy in the spring.
- The potential energy of the spring is maximum when it is fully stretched out.
When the spring is compressed:
- When a spring is compressed, it is shortened.
- Compressing the spring also requires work, which is stored as potential energy in the spring.
- The potential energy of the spring is maximum when it is fully compressed.
Conclusion:
Based on the above explanations, it can be concluded that the spring will have maximum potential energy when it is both pulled out and compressed. Therefore, option C: "both (a) and (b)" is the correct answer.

The energy possessed by an oscillating pendulum of a clock is:
The correct answer is (D) mechanical energy.
Explanation:
The energy possessed by an oscillating pendulum of a clock is a combination of kinetic energy and potential energy.
1. Kinetic energy:
- The pendulum of a clock swings back and forth, and as it swings, it possesses kinetic energy.
- Kinetic energy is the energy of motion and is given by the formula KE = 1/2 mv^2, where m is the mass of the pendulum and v is its velocity.
- As the pendulum swings from one extreme to the other, its velocity changes, and therefore its kinetic energy also changes.
2. Potential energy:
- At the extremes of its swing, the pendulum reaches its highest point, where it has the maximum potential energy.
- Potential energy is the energy that an object possesses due to its position or state.
- In the case of the pendulum, its potential energy is highest when it is at the highest point of its swing, and it decreases as it moves towards the lowest point.
3. Mechanical energy:
- Mechanical energy is the sum of kinetic energy and potential energy.
- As the pendulum swings back and forth, its mechanical energy is constantly changing, but the total amount of mechanical energy remains constant.
- This conservation of mechanical energy is due to the interplay between the pendulum's kinetic energy and potential energy.
Therefore, the energy possessed by an oscillating pendulum of a clock is (D) mechanical energy, which is a combination of kinetic energy and potential energy.

The gravitational potential energy of an object is due to:
There are several factors that contribute to the gravitational potential energy of an object. These include:
1. Mass: The mass of an object plays a significant role in determining its gravitational potential energy. Objects with greater mass have a greater potential energy due to gravity.
2. Acceleration due to gravity: The acceleration due to gravity, denoted as 'g', is a constant value that determines the strength of the gravitational force. The higher the acceleration due to gravity, the greater the potential energy of an object.
3. Height above the Earth's surface: The height of an object above the Earth's surface also contributes to its gravitational potential energy. Objects at higher altitudes have greater potential energy due to the increased distance from the center of the Earth.
Therefore, the gravitational potential energy of an object is due to its mass, acceleration due to gravity, and height above the Earth's surface. Hence, the correct answer is option D: all of the above.

The answer to the question is C: The potential energy decreases and the kinetic energy increases during the fall.
Explanation:

When the ball is dropped from a height of 10 m, it undergoes a change in energy as it falls. This change in energy can be explained by the concepts of potential energy and kinetic energy.
Potential Energy:

Potential energy is the energy possessed by an object due to its position or height above the ground. In this case, when the ball is at a height of 10 m, it has potential energy due to its position relative to the ground.
Kinetic Energy:

Kinetic energy is the energy possessed by an object due to its motion. As the ball falls, its potential energy decreases and is converted into kinetic energy.
Energy Transformation:

As the ball falls, the following energy transformation occurs:
- Initially, the ball has maximum potential energy and zero kinetic energy.
- As it falls, the potential energy decreases while the kinetic energy increases.
- At the midpoint of the fall, the potential energy and kinetic energy are equal.
- At the instant before it hits the ground, the potential energy is minimum (almost zero) and the kinetic energy is maximum.
Conclusion:

Based on the above explanation, we can conclude that during the fall of the ball from a height of 10 m, the potential energy decreases and the kinetic energy increases.

To understand why the kinetic energy of a body is quadrupled when its velocity is doubled, we can consider the relationship between kinetic energy (KE) and velocity (v) using the formula:
KE = (1/2)mv^2
Where:
- KE is the kinetic energy
- m is the mass of the body
- v is the velocity of the body
Now, let's consider the scenario where the velocity of the body is doubled:
1. Initial velocity: v
2. Final velocity: 2v
To find the ratio of the final kinetic energy (KE') to the initial kinetic energy (KE), we can substitute the final velocity (2v) into the kinetic energy formula:
KE' = (1/2)m(2v)^2
= (1/2)m(4v^2)
= 2mv^2
Comparing KE' to KE, we can see that the final kinetic energy (KE') is four times the initial kinetic energy (KE). Therefore, the correct answer is D: becomes 4 times.
In summary, when the velocity of a body is doubled, the kinetic energy quadruples because the kinetic energy is directly proportional to the square of the velocity.

Given:
- Work = 520 J
- Rate of work = 20 W
To find:
- Time required to perform the work

- The formula for work is given by: Work = Power x Time
- Rearranging the formula, we get: Time = Work / Power
Substituting the given values:
- Time = 520 J / 20 W
- Time = 26 seconds
Therefore, the time required to perform 520 J of work at the rate of 20 W is 26 seconds (option D).

Mass = 5kg S = 2m
Force = m × g= 5×10= 50N
Work = force × displacement W = 50 × 2W = 100 J

Explanation:
The work done on a body is defined as the product of the force applied on the body and the displacement of the body in the direction of the force. In this case, the work done is '0', which means there is no net transfer of energy to or from the body.
To understand why the work done is '0', let's consider the options one by one:
A: The body shows displacement in the opposite direction of the force applied.
- In this case, the work done will be negative because the displacement is in the opposite direction of the force. So, option A is not correct.
B: The body shows displacement in the same direction as that of the force applied.
- In this case, the work done will be positive because the displacement is in the same direction as the force. So, option B is not correct.
C: The body shows a displacement in perpendicular direction to the force applied.
- In this case, the work done will be zero because the displacement is perpendicular to the force. This means that there is no component of the force in the direction of displacement, and hence no work is done. So, option C is correct.
D: The body masses obliquely to the direction of the force applied.
- This option is not clear and seems to have a typographical error. It is difficult to understand what is meant by "the body masses obliquely to the direction of the force applied". Therefore, option D is not a valid option.
Thus, the correct answer is option C: The body shows a displacement in perpendicular direction to the force applied.

Explanation:
To determine the correct answer, we need to understand the definition of electrical energy and its unit of measurement.
- Electrical energy is the amount of work done by an electric current in a given amount of time.
- The SI unit for electrical energy is the joule (J).
Now, let's evaluate each option and determine which one is equal to one unit of electrical energy:
A:

3.6 × 10⁵ J

- This option is equal to 360,000 joules. It is not equal to one unit of electrical energy.
B:

3.6 × 10⁶ J

- This option is equal to 3,600,000 joules. It is not equal to one unit of electrical energy.
C:

360 × 10⁵ J

- This option is equal to 36,000,000 joules. It is not equal to one unit of electrical energy.
D:

3.6 × 10^-6 J

- This option is equal to 0.0000036 joules. It is not equal to one unit of electrical energy.
Based on the evaluation above, none of the given options is equal to one unit of electrical energy. Therefore, none of the options are correct.
The correct answer is not provided in the given options.