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Question
A boy of mass 40 kg runs up a height of 30 steps, each 20 cm high. Find:
(i) The force of gravity acting on the boy.
(ii) The work done by the boy against gravity. (Take g = 9.8 ms−2)
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Solution
Given : m = 40 kg, g = 9.8 ms−2
Distance moved, d = 30 × 20 cm = 600 cm = 6 m.
(i) The force of gravity, F = mg = 40 × 9.8 = 392 N.
(ii) The work done by the boy, W = F × d = 392 × 6 = 2352 J.
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