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JEE Main 2019 (9 Jan, Shift 2) · Doppler Effect

Doppler Effect question from JEE Main 2019 (9 Jan, Shift 2)

Q56JEE Main 2019 · 9 JAN · SHIFT 2Medium

Doppler Effect

A musician using an open flute of length 50 cm producess second harmonic sound waves. A person runs towards the musician from another end of hall at a speed of 10 km/h. If the wave speed is 330 m/s, the frequency heard by the running person shall be close to:

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Answer: (a)

Open pipe, second harmonic: $f = \dfrac{2v}{2L} = \dfrac{2 \times 330}{2 \times 0.5} = 660\text{ Hz}$ .
Runner speed $u = 10\text{ km/h} \approx 2.78\text{ m/s}$ .
$f' = 660 \times \dfrac{330 + 2.78}{330} \approx 665.6\text{ Hz}$
So the answer is (a) 666 Hz.

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