Question

What do you mean by echo. A boy hears the echo of his own voice from a distant hill after 0.8 second. If the speed of sound in air 340 m/s. Calculate the distance of the hill from the boy .

Answer 1

What do you mean by echo?

Echo can be defined as the repeated sound cause by the reflection of the sound from any surface. This phenomenon occurs in $1/10^{th}$ of the second and wavelength of sound is 17.2 m(speed of the sound is 344 m/s).

Given:-

$v(sound)=340m/s\\time= 0.8s\\v=\frac{2d}{t} \\\frac{2d}{0.8}=340\\2d=340*0.8\\2d=272\\d=136$

Therefore,the distance between the boy and the hill is 136m

Formula used here:- $v=\frac{2d}{t}$

Here 2d is used because the sound is hitting and reaching back to the boy's ears.

Verification:-

$v=\frac{2d}{t}\\v=\frac{2*136}{0.8}\\v=\frac{272}{0.8}\\v=\frac{272*10}{8}\\v=340m/s$

So, here is the answer, hope it may help.