Question

A stone is dropped from the top of the tower 125m high into a pond of water at the base of the tower. When is the splash heard at the top? Given, g = 10 m/s and speed of sound = 342m/s.

Answer 1

Time taken by the stone to reach the water :

assuming downward direction as positive,
$s = ut + at ^{2} /2$
125 = 0(t) + 10($t^{2}$/2
t = 5 seconds

Time taken by the sound wave to reach the top of the tower after the stone hits the water:

s= ut ;    125 = 342t ;   t = 125/342 = 0.36549 s 

Time taken for the splash to be heard at the top = 5.36549 s