Question

A pendulum has a frequency of 5 vibrations per second. An observer starts the pendulum and fires a gun simultaneously .He hears the echo from the cliff after 8 vibrations of the pendulum .if the velocity of sound in air is 340m/s find the distance between the cliff and the observer? plz dolve it completely

Answer 1

A pendulum has a frequency of 5 vibrations per second. 
This statement says:
Time took by a pendulum for 1 vibration = 1/5 sec
Then, Time take by a pendulum for 8 vibration =8/5 sec
We know that,
2d = vt
then, d = vt/2
Put values: You will get this...         
         d = 272 m
 ∴ the distance between the cliff and the observer will be 272 m.