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JEE Main 2015 (10 Apr, Shift 1) · Doppler Effect

Doppler Effect question from JEE Main 2015 (10 Apr, Shift 1)

Q65JEE Main 2015 · 10 APR · SHIFT 1Medium

Doppler Effect

A bat moving at 10 ms ${}^{-1}$ towards a wall sends a sound signal of 8000 Hz towards it. On reflection it hears a sound of frequency f. The value of f in Hz is close to (speed of sound = 320 ms ${}^{-1}$ )

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Answer: (b)

Echo heard by the bat moving towards the wall: $f = f_0\,\dfrac{v + u}{v - u}$ .
$f = 8000 \times \dfrac{330}{310} \approx 8516\text{ Hz}$
So the answer is (b) 8516 Hz.

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