Question

A stone is dropped in a well of depth 500 m and a sound is heard after 45/4 seconds. Then speed of sound is (if g = 10 m/s2)?

Answer 1

first of all, we should find time taken by stone to reach 500m depth in well.

here, S = -500m [ we take reference level is in initial position of stone]

u = 0, a = -g = -10m/s²

use formula , S = ut + 1/2 at²

-500 = 0 - 1/2 × 10 × t²

t² = 100 => t = 10sec

but sound is heard after 45/4 = 11.25 sec

hence, time taken to reach 500m depth = 11.25 -10 = 1.25 sec .

now speed of sound = distance/time

= 500/1.25 = 400 m/s