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A train is moving at a speed of 72 kmph ...

A train is moving at a speed of 72 kmph towards a station sounding a whistle of frequency 640Hz. What is the apparent frequency of the whistle as heard by a man standing on the platform when train approaches towards him.

Text Solution

Verified by Experts

`V_(S)= 72 "kmph" = 20 "ms"^(-1), f= 640 "Hz," V = 340 "ms"^(-1)`
W.K.T apparent frequency
`f = (fv)/(V-V_(S))= (640 xx 340)/(340-20)= (640 xx 340)/(320) " " therefore f= 680 Hz`
Apparent frequency of sound as heard by the observed will be 680 Hz.
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