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Question: The source of sound s is moving with a velocity 50 m/s towards a stationary observer. The observer m...

The source of sound s is moving with a velocity 50 m/s towards a stationary observer. The observer measures the frequency of the source as 1000 Hz. What will be the apparent frequency of the source when it is moving away from the observer after crossing him ? The velocity of sound in the medium is 350 m/s

A

750 Hz

B

857 Hz

C

1143 Hz

D

1333 Hz

Answer

750 Hz

Explanation

Solution

When source is moving towards the stationary listener.

n′=vv−vsn⇒1000=350350−50.n⇒n=857.14n' = \frac{v}{v - v_{s}}n \Rightarrow 1000 = \frac{350}{350 - 50}.n \Rightarrow n = 857.14When source is moving away from the stationary observer n′′=vv+vs\mathbf{n'' =}\frac{\mathbf{v}}{\mathbf{v +}\mathbf{v}_{\mathbf{s}}}= 350350+50×857\frac{\mathbf{350}}{\mathbf{350 + 50}}\mathbf{\times}\mathbf{857}= 750 Hz