Question

Kendra separately pushes two boxes in a straight line at constant velocity over the same distance on level ground. Each box begins and ends at rest. Kendra exerts no force to stop either box; friction brings them both to rest. The contact surfaces and areas between each box and the floor are the same for both, but one box is heavy and the other is light.
Which of the statements is correct?

A) Kendra does the same amount of work on both boxes, and the same amount of net work is also done on both boxes.

B) Kendra does more work on the heavy box, and more net work is also done on the heavy box.

C) Kendra does more work on the heavy box, but the net work done on both boxes is equal.

D) Kendra does the same amount of work on both boxes, but more net work is done on the heavy box.

E) Kendra does more work on the light box, but more net work is done on the heavy box.

Answer 1

Kendra does more work on the heavy box, and more net work is also done on the heavy box.

Explanation:

While exerting force to move the two boxes, Kendra exerts two different amounts of force (i.e. higher magnitude of force for heavier box and vice versa). On account of opposing frictional force, the boxes stop after some time.

We know Work done= F*D

∵ Where F= force applied  

           D= Distance moved

Since the distance moved is same in both the cases hence work done would be dependent on the force applied only.

Force= m*a

Where m= mass of the box and a= acceleration

Here Mass of the heavy box would be more than the lighter box

∴ Force applied on the heavier box would be more than on the lighter box

∵Work done by heavier box would be more as compared to the lighter box.