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Work, Energy and Power
The sign of work done by a force on a body is important to understand. State carefully if the following quantities are positive or negative:
(d) work done by an applied force on a body moving on a rough horizontal plane with uniform velocity
Positive quantity.
In this case, the body is moving on a rough horizontal plane. Frictional force opposes the motion of the body. Therefore, in order to maintain a uniform velocity, a uniform force must be applied to the body. Since the applied force acts in the direction of motion of the body, the work done is positive.
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By eating two apples, a person starts pushing the wall of room. If food value of apple is 100 calories per apple, how much work he will do in pushing the wall in one hour?
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