Question

a boy is playing with a ball on the roof of a building 480 m high from the ground. Suddenly the ball slips from his hand and falls into a well on the ground. The water level in the the well is 20m below the ground,and he hears the sound of the ball hitting after 11.5 sec from the instant of slip. The speed of sound in air is ( take g=10 m/s^2)

Answer 1

The speed of sound in air will be 333.33 m/s

Explanation :

net height to which the ball falls = 480 + 20 = 500 m

from the laws of motion we know that,

S = ut + at²/2

given S = 500 m

u = initial velocity = 0

a = g = 10 m/s²

=> 500 = 0 + 5t²

=> t² = 100

=> t = 10 sec

So the ball will take 10 sec to fall into the water

Hence time taken by the sound waves to reach the boy's ear

= 11.5 - 10

= 1.5 sec

Hence speed of the sound = 500/1.5 = 333.33 m/s