A box is pushed across a rough horizontal surface at a constant speed by a small child. Which object does negative work on the box: (a) the child, (b) the surface, or (c) the earth?
The object doing negative work.
Answer to Problem 1CQ
Option (b) the surface
Explanation of Solution
The child pushes the box across a rough horizontal surface with constant speed. The surface, being rough opposes the motion due to the presence of frictional force. Work is negative when the direction of motion is opposite to the applied force.
Since the frictional force opposes the direction of applied force, work is negative. The earth doesn’t come into the picture of motion of box across the rough surface. Therefore, option (b) is correct.
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