A pendulum has a frequency of 4 vibrations per second. An observer starts the pendulum and fires a gun simultaneously. He hears the echo from the cliff after 6 vibrations of the pendulum. If the velocity of sound in air is 340 m/s, find the distance between the cliff and the observer.

Explanation

Time taken to complete 4 vibrations = 1 second
Time taken to complete 1 vibration = `1/4` second
`therefore` Time taken to complete 6 vibrations
= `1/4xx6` second
= 1.5 second
Time (t) = 1.5 s
Velocity (v) = 340 m/s
`therefore` Distance between the cliff and observer
`d=(vxxt)/2`
`=(340xx1.5)/2m`
= 255 m