Question

1. A man standing between two cliffs produces a sound and hears two successive echoes at intervals of 3s and 4 s respectively. Calculate the distance between the two cliffs. The speed of sound in the air is 330ms^-1 . 

2. Why will an echo not be heard when the distance between the source of sound and the reflecting surface is 10 m?

Answer 1

Loud sound is produced during resonance, but not in case of forced vibrations.

Distance between AB = x + y = 495 + 660 = 1155m

The persistence of sound on ear drum is 1/10 of a second. The echo can be heard if the minimum distance of the source of sound from the vibrating body is 17m. As the distance is only 10m, therefore, no echo is produced.