Question

the echo of a sound is heard after 5 sec. if the speed of sound in air be 342 m/s, calculate the distance of the reflecting surface.

Answer 1

The required answer is 855 metres. Thanks!

Answer 2

What we need to understand is that the sound travels to the reflecting surface  and back before it is heard.

This means that if the distance to the reflecting surface is d then for the sound to be heard the distance traveled will be 2d.

The following formula is relevant :

Speed = Distance / Time

Distance = Speed × time

The distance traveled by the sound is thus :

Distance = 5 × 342 = 1710 meters.

Remember if the distance to the reflecting surface is d then the distance covered by the sound is 2d.

Therefore :

2d = 1710

d = 1710/2 = 855 m

The distance of the reflecting surface is therefore :

855 meters