Question

$ A $ and $ B $ are two hills at a distance $510\, m$ apart. A person standing between the hills claps his hands and hears two echoes at the end of $1\, s$ and $2\, s$ respectively. The velocity of sound in air is:

• A. 225 m/s
• B. 340 m/s
• C. 510 m/s
• D. 1020 m/s

Answer 1

Answer: (B)

Time taken by echo to reach the person is directly proportional to distance.
Let distance of person from hill $A$ be $x$ meter, then from hill $B$ is $(510-x)m$.

$\therefore \frac{x}{510-x}=\frac{\text{(time)}_{1}}{\text{(time)}_{2}}=\frac{1}{2} $
$\Rightarrow x=170 \,m$
Time taken for the echo to travel $170\, m$ is given by
$\frac{1}{2}=0.5\, s$
$\therefore $ Velocity $=\frac{\text { distance }}{\text { time }} $
$=\frac{170}{0.5} $
$=340 \,m / s$