Work Energy and Power Test

Result

Work Energy and Power Test - 2

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Question 1
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A body is falling freely under the action of gravity alone in vacuum. Which of the following quantities remain constant during the fall?

A
Kinetic energy.

B
Potential energy.

C
Total mechanical energy.

D
Total linear momentum.

Solution

When a body is under free fall, only force due to gravity is acting on the body. The body is accelerating so the kinetic energy of the body is changing along with the potential energy since the height of the falling body is constantly changing every moment as the body fall towards the earth.

Therefore, option A and B does not remain constant during the free fall.

The total mechanical energy of body moving, is equal to the sum of the kinetic energy and the potential energy. The kinetic energy and the potential energy although do not remain constant itself, the sum of the two energies will remain constant as the total mechanical energy of a body under free fall remains constant.
Question 2
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Caleb increases the force applied on a crate to push it faster across a floor. How does work done by crate and kinetic energy relate in this case?

A
The net-work done on the crate is equal to the initial kinetic energy

B
The net-work done on the crate is equal to the change in its kinetic energy

C
The net-work done on the crate is greater than the change in its kinetic energy

D
The net work done on the crate is less than change in its kinetic energy.

Solution

Caleb increases the force acting on the crate. The increase in the magnitude of the force exerted on the crate increases its speed. In turn, the velocity of the crate also increases.
Although, according to the work-energy theorem, the change in kinetic energy must be equal to the net work done on the crate, therefore, the change in the kinetic energy is equal to the net work done