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JEE Main 2022 (28 Jul, Shift 1) · Doppler Effect

Doppler Effect question from JEE Main 2022 (28 Jul, Shift 1)

Q39JEE Main 2022 · 28 JUL · SHIFT 1Easy

Doppler Effect

The frequency of echo will be __________ Hz if the train blowing a whistle of frequency 320 Hz is moving with a velocity of 36 km/h towards a hill from which an echo is heard by the train driver. Velocity of sound in air is 330 m/s.

Numerical answer type. Work it out, then open the answer.

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Answer: 340

Train speed $u = 36\text{ km/h} = 10\text{ m/s}$ .
Echo heard by the driver: $f' = f\,\dfrac{v+u}{v-u} = 320 \times \dfrac{340}{320}$
$f' = 340\text{ Hz}$

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