Class 11 NEET Physics Waves Questions Questions

The whistle is revolving in a circle of radius 50cm. So the source (whistle) is moving and the observer is fixed.The minimum frequency will be heard by the observer when the linear velocity of the whistle (source) will be in a direction as shown in the figure, i.e. when the source is receding.
The apparent frequency heard by the observer is then given by v′=v(

v

V+v

)
where V and v are the velocities of sound and source respectively and v is the actual frequency.
Now, v=rω=0.5×20=10m∕s
V=340m∕s,v=385Hz
∴v′=385×

340

340+10

=374Hz