Question

A pebble is dropped freely in a well from its top. It
takes 20 s for the pebble to reach the water surface
in the well. Taking 8 = 10 m 52 and speed of
sound = 330 m , find : (i) the depth of water
surface, and (ii) the time when echo is heard after
the pebble is dropped.​

Answer 1

Solution :-

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Time taken by the ball to hot the water surface = 20 sec

Initial velocity  = 0  , acceleration = g = 10m/s²

The height of well = H

s  = ut + 1/2 a t²

H = 0 +1/2 × 10×20×20

H = 2000 meter

When pebble strikes the surface then sound is produced and it comes to observer by travelling the distance of the well.

Velocity of sound = 332 m/s , distance = H = 2000 m

time taken by sound to come to observer = t = distance/speed = 2000/332 = 6.02seconds.

The sound will be heard after 20 + 6.02  = 26.02 seconds.

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