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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:
(c) work done by friction on a body sliding down an inclined plane
Negative quantity
The direction of the frictional force is opposite to the direction of motion. Therefore, the work done by the frictional force is negative in this case.
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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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