Question

22. The driver of a car approaching a vertical wall notices
that the frequency of his car's horn changes from 440 Hz
to 480 Hz when it gets reflected from the wall. Find the
speed of the car if that of the sound is 330 ms.​

Answer 1

For the driver of the car ,wall serves as the source of sound .

Let the speed of the car be v .

This is the case when the source of sound is stationary and the observer is moving .

So , the apparent frequency f' heard by the observer is given as :

f'=vsound+vobservervsound×ff'=vsound+vobservervsound×f

here,

480=330+v330×440⇒360=330+v⇒v=30 m/s