A man stationed between two parallel cliffs fires a gun . He hears the first echo after 1.5s and the next after 2.5s. What is the distance between the cliffs and when does he hear the third echo? Take the speed of sound in air as 340m/s .
Suppose the two cliffs are A and B which are at the distances x and y from the man respectively.
Consider that the echo of 1.5 sec and 2.5 sec are produced by are produced by cliff A and B.
2x = 340 x 1.5
x = 255 m
2y = 340 x 2.5
y = 425 m
Distance between the cliff = x + y = 680 m
The third echo will be heard after 1.5 sec from the time when the second echo is heard.