Question

A boy plays with a ball and he drops it from a height of 1-5 m. Every time the ball hits the ground, it bounces back to attain a height 4/5th of the previous height. The ball does not bounce further if the previous height is less than 50 cm. What is the number of times the ball hits the ground before the ball stops bouncing?

(a) 4

(b) 5

(c) 6

(d) 7

Answer 1

Correct option is (c) 6

Initial height of the drop = 1.5 m = 150 cm

Drop	Previous Height(cm)	Height after Bouncing Back(cm)
1	150	150 × 4/5 = 120
2	120	120 × 4/5 = 96
3	96	96 × 4/5 = 76.8
4	76.8	76.8 × 4/5 = 61.44
5	61.44	61.44 × 4/5 = 49.152
6	49.152	0

So, the ball touches the ground for 6 times.

Answer 2

The number of times the ball hits the ground before the ball stops bouncing is

(b) 5

the ball hits the ground from heights 150cm, 120cm, 96cm, 76.8cm, and 61.44cm