Question

A pebble is dropped freely in a well from its top . it takes 20 s for the pebble ti reach the water surface in the well . find the time when the echo is heard after the pebble is dropped let the g is 10 m/s

Answer 1

Total time taken for the echo to be heard = 25.88 seconds

Time taken to hear the splash of water = time taken by the stone to reach the water in well + time taken by the sound of splash to reach the listener

Given, time taken for the pebble to reach the water surface = 20 seconds

u = 0

s = depth of the well

g = 10 m/s²

Using , s = ut + 1/2 gt²

=> s = 0 + 1/2 × 10 × t²

=> s = 5 × 400

=> s = 2000 m

For the time taken by the sound of splash to reach the listener -

v = 340 m/s = velocity of sound

s = 2000 m

s = vt'

=> t' = 2000/340

=> t' = 5.88 seconds

Total time taken = t + t'

= 20 + 5.88

= 25.88 seconds