Question

Let the distance of reflecting surface from the sound source and observer be d and speed of sound in air be v, then the time of echo is:

• A. t = d/2v
• B. t = 2d x v
• C. t = 2d / v
• D. t = d / v

Answer 1

The correct option is C

t = 2d / v

Total distance covered by sound before echo is heard is twice the distance of obstacle.
$s$

Speed of sound is $v$

Let the time for the echo to be heard be $t$.
From definition of speed,
$v=\frac{s}{t}$
$t=2d/v$