Question

A mass of 30 g falls from a height of 16 m and after striking the ground,

it rebounds to a height of 12 m. Calculate:

a) The kinetic energy of the ball just before striking the ground.

b) Loss in kinetic energy of the ball on striking the ground.

c) What happens to the loss in kinetic energy?
Take g = 10 ms-2​

Answer 1

Question :

A ball of mass 20g falls from a height of 10m and after striking the ground, it rebounds from the ground to a height of 8m. Calculate a)The kinetic energy of the ball just before striking the ground. b)Loss in kinetic energy of the ball on striking the ground. c)What happens to the loss in kinetic energy in part b).

Solution :

Given :-

Mass (m) = 20g = 20/1000Kg = 0.02Kg

Height (h) = 10m

Height¹ (h¹) = 8m

Acc. due to gravity (g) = 10m/s²

Explanation :-

a) The kinetic energy just before striking the ground is equal to the initial potential energy of the ball

• mgh = 0.02 × 10 × 10
• 2 J

b) The kinetic energy of the ball just after striking the ground is equal to the potential energy of the ball at the highest point after rebound.

• mgh¹ = 0.02 × 10 × 8
• 1.6 J

∴ Loss in K.E on striking the ground is equal to K.E of the ball just before striking the ground - K.E of the ball just after striking the ground.

• 2J - 1.6J
• 0.4 J

c) The loss in K.E in part b) appears in the form of heat and sound energies when the ball strikes the ground.