Question

A body shouts inside a deep well and hears the echo 0.4 s after shouting. if the speed of sound is 340 $m{s}^{-1}$ find the depth of the water level in the well :

• A. 78 m
• B. 88 m
• C. 68 m
• D. 58 m

Answer 1

Answer: (C)

68 m

Let d be the distance of body from water level in well (depth of water level) , therefore total distance travelled by sound wave , $=2d$ , as the wave comes back after reflection so the distance will be doubled .

Now given , $v=340m/s,t=0.4s$ ,

therefore , by , total distance =velocity $\times$ total time

$2d=v\times t$ ,

or $d=v\times t/2=340\times 0.4/2=68m$