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Question
A boy weighing 50 kgf climbs up from the first floor at a height of 3 m above the ground to the third floor at a height of 9 m above the ground. What will be the increase in his gravitational potential energy? (Take g = 10 N kg-1).
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Solution
Force acting on body = 50 kgf
= [50 kg × 10] N
= 500 N
As height change from 3 m to 9 m
∴ Increase in energy in, rising from 3 m to 9 m above the ground = mgh2 – mgh1
= mg [h2 – h1]
= 500 [9 – 3]
= 500 × 6
= 3000 J
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