Question

A ball of mass m is dropped freely from point A. It is given that AB = BC = CD = h. If the acceleration due to gravity at the given place is g, then what will be its

1. potential energy at point A?
2. kinetic energy at point C?

Answer 1

(a) Taking the ground at D as the zero level of potential energy.

Point A is 3h above the ground.

Therefore, potential energy at A = mg(3h) = 3mgh.

(b) The ball falls from rest through a distance AC = AB + BC = 2h before reaching C.

By conservation of energy, the loss in potential energy becomes kinetic energy.

Hence, kinetic energy at C = mg(2h) = 2mgh.