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Question: Suppose that the speed of sound in air at a given temperature is 400 m/sec. An engine blows a whistl...

Suppose that the speed of sound in air at a given temperature is 400 m/sec. An engine blows a whistle at 1200 Hz frequency. It is approaching an observer at the speed of 100 m/sec. What is the apparent frequency as heard by the observer

A

600 Hz

B

1200 Hz

C

1500 Hz

D

1600 Hz

Answer

1600 Hz

Explanation

Solution

n′=n(vv−vS)=1200(400400−100)=1600Hzn' = n\left( \frac{v}{v - v_{S}} \right) = 1200\left( \frac{400}{400 - 100} \right) = 1600Hz