A boy weighing 50 kg climbs up a vertical height of 100 m. Calculate the amount of work done by him. How much potential energy does he gain? (g = 9.8 m/s²)

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Solution

(i) Mass of the boy, (m) = 50 kg
Height above the ground, (h) = 100
Acceleration due to gravity, (g) = 9.8 m/s²
We can calculate the work done against gravity as,
Work done in lifting a body = (Weight of body) × (Vertical distance)
So, W = m × g × h
So work done,
W = 50 × 9.8 × 100 J
= $49 KJ$
Now, potential energy of a body kept at the same height is equal to the amount of work done against gravity in moving the body to that position. Therefore, the potential energy of the boy at that height is $49 KJ$

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