A bus is moving towards a huge wall with a velocity of `5 m//s`. The driver sounds a horn of frequency `200 Hz`. The frequency of the beats heard by a passenger of the bus will be _____Hz. (Speed of sound in air `= 342 m//s`).

Explanation

The first frequency the driver of bus hears is the original frequency 200 Hz. The second frequency the driver hears is the frequency of sound reflected from the wall. The two frequencies of sound heard by the driver are
I. Original frequency (200Hz)
II. Frequency of sound reflected from the wall (v')
The frequency of sound reflected from the wall
`v'=v[(u+u_(0))/(u-u_(s))]`
`v'=200[(342+5)/(342-5)]=205.93Hz`
`therefore`Frequency of beats=v'=v=205.93-200=5.93=5Hz