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A boy of mass kg runs upstairs and reaches the 8 m high floor in 5 s Calculate:the force of gravity acting on the boy.(i) the work done by him against gravity.(ii) the power spent by boy.(Take g = 10 m s-2) |
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Answer» Mass of boy = 40 kg Vertical height moved, h = 8m Time taken, t = 5s. (i) Force of gravity on the boy F = mg = 40 × 10 = 400N (ii) While climbing, the boy has to do work against the force of gravity. Work done by the boy in climbing= Force × distance moved in the direction of force Or, W = F x S= 400 x 8= 3200 J Power spent = work done/time taken = 3200/5 = 640 W |
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