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NEET 2004 (AIPMT) · Doppler Effect

Doppler Effect question from NEET 2004 (AIPMT)

Q78NEET 2004 · AIPMTEasy

Doppler Effect

A car is moving towards a high cliff. The driver sounds a horn of frequency $f$ . The reflected sound heard by the driver has frequency $2f$ . If v is the velocity of sound, then the velocity of the car, in the same velocity units, will be

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Answer: (b)

Echo from a cliff heard by a driver moving at $u$ : $f' = f\,\dfrac{v+u}{v-u}$ .
$f' = 2f \Rightarrow v + u = 2v - 2u \Rightarrow 3u = v$
So the answer is (b) $u = v/3$ .

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