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NEET 2009 (AIPMT) · Doppler Effect

Doppler Effect question from NEET 2009 (AIPMT)

Q74NEET 2009 · AIPMTEasy

Doppler Effect

The driver of a car travelling with speed 30 m/s towards a hill sounds a horn of frequency 600 Hz. If the velocity of sound in air is 330 m/s, the frequency of reflected sound as heard by driver is

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Answer: (b)

The hill receives the horn from a source approaching it, then reflects it back to the driver, who is an observer approaching the hill.
$n' = n\frac{v + v_c}{v - v_c}$
$n' = 600 \times \frac{330 + 30}{330 - 30} = 600 \times \frac{360}{300} = 720$ Hz
So the answer is (b) 720 Hz.

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