The engine of a train moving with speed 10 ms⁻¹ towards a platform sounds a whistle at frequency 400 Hz. The frequency heard by a passenger inside the train is: (neglect air speed. Speed of sound in air = 330 ms⁻¹) (a) 200 Hz (b) 412 Hz (c) 400 Hz (d) 388 Hz

Answer: (c). The passenger moves with the engine at the same velocity, so there is no relative motion between source and listener. No Doppler shift: frequency heard = 400 Hz. So the answer is (c) 400 Hz.

The engine of a train moving with speed 10 ms⁻¹ towards a platform… | JEE Main 2023 (8 Apr, Shift 1)

Q33JEE Main 2023 · 8 APR · SHIFT 1Easy

Doppler Effect

The engine of a train moving with speed $10\text{ ms}^{-1}$ towards a platform sounds a whistle at frequency $400\text{ Hz}$ . The frequency heard by a passenger inside the train is: (neglect air speed. Speed of sound in air $= 330\text{ ms}^{-1}$ )

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Answer: (c)

The passenger moves with the engine at the same velocity, so there is no relative motion between source and listener.
No Doppler shift: frequency heard $= 400$ Hz.
So the answer is (c) 400 Hz.

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