Question

A man standing $25m$ away from a wall produces a sound and receives the reflected sound.
(a) Calculate the time after which he receives the reflected sound if the speed of sound in air is $350m{s}^{-1}.$
(b) Will the man be able to hear a distinct echo ? Explain .

Answer 1

For echo, total distance travel by sound = $2D$

(a) Velocity $=\frac{2D}{Time}$

Time $=\frac{2\times 25}{350}=0.143seconds$
(b) Yes, because the reflected sound reaches the man $0.1$ second after the original sound is heard and the original sound persists only for $0.1$ second.