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JEE Main 2019 (10 Apr, Shift 1) · Doppler Effect

Doppler Effect question from JEE Main 2019 (10 Apr, Shift 1)

Q55JEE Main 2019 · 10 APR · SHIFT 1Medium

Doppler Effect

A stationary source emits sound waves of frequency 500 Hz. Two observers moving along a line passing through the source detect sound to be of frequencies 480 Hz and 530 Hz. Their respective speeds are, in ms–1, (Given speed of sound = 300 m/s)

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Answer: (a)

480 Hz is lower, so that observer moves away: $480 = 500\,\dfrac{300 - u_1}{300} \Rightarrow u_1 = 12\text{ m/s}$ .
530 Hz is higher, so that observer moves towards: $530 = 500\,\dfrac{300 + u_2}{300} \Rightarrow u_2 = 18\text{ m/s}$ .
So the answer is (a) 12, 18.

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