Question

A splash is heard after $3$ second after the stone is dropped into a well of depth $20m$. The velocity of sound is:

• A. 18 m / s
• B. 28 m / s
• C. 20 m / s
• D. 19 m / s

Answer 1

Answer: (C)

Stone is dropped, $u=0$
Let $t$ is the time taken by the stone to cover depth of $20m$.
$20=ut+\frac{1}{2}g{t}^2\Rightarrow 20=\frac{1}{2}\times 10\times t^2$
$t=2$
Splash heard after $3$ second but time taken by stone is $2$ second
$\therefore \Delta t=3-2=1$ second
or velocity of particle $=20/1=20m/s$