Question

What should be the minimum distance between the listener and the reflector to hear an echo of sound propagating with a speed $vm{s}^{-1}$?

• A. $v/10$ m
• B. $10v$ m
• C. $v/20$ m
• D. $20v$ m

Answer 1

The correct option is C $v/20$ m

if there is a sound reflector at a distance d from the source, then the time interval between original sound and its echo at the site of the source is given as $T=\frac{2d}{v}$

$d=\frac{v\times t}{2}=\frac{v\times 1}{2\times 10}$ as Time = 0.1 s.

Hence, $d=\frac{v}{20}$.