Question

A boy standing between two cliffs claps and hears 2 echoes after 2s and 2.5 s respectively. If the velocity of sound is 330 $m{s}^{-1}$, find the distance between he two cliffs :

• A. 742.50 m
• B. 274.50 m
• C. 472.50 m
• D. 442.50 m

Answer 1

The correct option is A 742.50 m

Let $d_1$ and $d_2$ be the distances of cliffs from the boy .

for first echo , which is heard after $2s$ ,

total distance travelled by sound $=2d_1$ ,

given $v=330m/s$ ,

we have , distance=speed$\times$time ,

$2d_1=330\times 2$ ,

or $d_1=660/2=330m$ ,

for second echo , which is heard after $2.5s$ ,

total distance travelled by sound $=2d_2$ ,

given $v=330m/s$ ,

we have , distance=speed$\times$time ,

$2d_2=330\times 2.5$ ,

or $d_2=825/2=412.5m$ ,

therefore , distance between cliffs , $d=d_1+d_2=330+412.5=742.5m$