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

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

Q52JEE Main 2019 · 9 APR · SHIFT 2Easy

Doppler Effect

Two cars A and B are moving away from each other in opposite directions. Both the cars are moving with a speed of 20 ms–1 with respect to the ground. If an observer in car A detects a frequency 2000 Hz of the sound coming from car B, what is the natural frequency of the sound source in car B?

(speed of sound in air = 340 ms–1) :-

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Answer: (c)

Moving apart: $n' = n\frac{v - v_o}{v + v_s}$ .
$2000 = n \times \frac{340 - 20}{340 + 20} = n \times \frac{8}{9}$
$n = 2000 \times \frac{9}{8} = 2250$ Hz. So the answer is (c) 2250 Hz.

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