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JEE Main 2022 · 30 Jun · Shift 1, Physics question 52

An employee of a factory moving away from his workplace by a car listens to the siren of the factory. He drives the car at the speed of 72 kmh−1^{-1} in the direction of wind which is blowing at 72 kmh−1^{-1} speed. Frequency of siren is 720 Hz. The employee hears an apparent frequency of ______ Hz.

(Assume speed of sound to be 340 ms−1^{-1})

Answer and worked solution

Official answer: 680

Doppler with wind (wind 20 m s−1^{-1} along the listener's motion, listener moving away at 20 m s−1^{-1}): f′=720×340+20−20340+20=680f'=720\times\dfrac{340+20-20}{340+20}=680 Hz.

Answer: 680

Topics:Doppler effect
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