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Question
A boy throws a rubber ball vertically upwards. What type of work, positive or negative, is done : by the force applied by the boy?
(a) by the force applied by the boy?
(b) by the gravitational force of earth?
Solution
A boy throws a rubber ball vertically upwards. Work done by the two forces:
(a) Work done by the force applied by the boy is positive because the displacement of the ball is in the direction of force applied.
(b) Work done by the gravitational force is negative because the displacement of the ball is opposite to the direction of gravitational force.
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