An echo is heard in 3 s. What is the distance of the reflecting surface from the source, given that the speed of sound is 342 m/s?

Speed of sound (v) = 342 m/s

Echo returns in time (t) = 3 s

Distance travelled by sound
=\( v × t = 342 × 3 = 1026 m \)

In the given interval of time, sound must travel a distance which is twice the distance of reflecting surface and source.

Therefore, the distance of reflecting surface from the source =\( \frac{1026}{2} = 513 m \).