Question

$A$ and $B$ are two hills at a distance $510m$ apart. A person standing between the hills claps his hands and hears two echoes at the end of $1s$ and $2s$ 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 $(510-x)m$.

$\therefore \frac{x}{510-x}=\frac{{\text{(time)}}_1}{{\text{(time)}}_2}=\frac{1}{2}$
$\Rightarrow x=170m$
Time taken for the echo to travel $170m$ is given by
$\frac{1}{2}=0.5s$
$\therefore$ Velocity $=\frac{\text{ distance }}{\text{ time }}$
$=\frac{170}{0.5}$
$=340m/s$