Question
A man standing in front of a vertical cliff fires a gun. He hears the echo after 3 seconds. On moving closer to the cliff by 82.5 m, he fires again. This time, he hears the echo after 2.5 seconds. Calculate:
i) The distance of the cliff from the initial position of the man.
ii) The velocity of the sound.
Solution
Let the distance of the cliff from the initial position of the man be ‘d’ m.
So, the distance travelled by sound in 3 sec = 2d m
So, speed of sound, S = 
On moving closer to the cliff by a distance of 82.5 m, the distance = 2 (d – 82.5) m.
So, 
... (2)
Therefore, from equations (1) and (2), 
