Question

The splash is heard after $2.05s$ after the stone is dropped into a well of depth $19.6$m the velocity of sound is:

• A. $342m{s}^{-1}$
• B. $372m{s}^{-1}$
• C. $392m{s}^{-1}$
• D. ${352}^{-1}$

Answer 1

The correct option is C $392m{s}^{-1}$

Given, $T=2.05,h=19.6m$

Let be the time taken by the stone to reach the well.

We know that,

$S=ut+\frac{1}{2}a{t}^2\Rightarrow 19.6=0\times t+0.5\times 9.8\times t^2\Rightarrow t^2=\frac{19.6}{4.9}=4\Rightarrow t=2s$

Then the time taken by the sound is equal to the taken by the stone is subtracted by total time,

$=2-0.5-2=0.5s\Rightarrow V=\frac{D}{T}=\frac{19.6}{0.5}=392m/s$