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NEET 2016 (Phase 1) · Doppler Effect

Doppler Effect question from NEET 2016 (Phase 1)

Q62NEET 2016 · PHASE 1Medium

Doppler Effect

A siren emitting a sound of frequency 800 Hz moves away from an observer towards a cliff at a speed of 15 m s−1{}^{-1}. Then, the frequency of sound that the observer hears in the echo reflected from the cliff is

(Take velocity of sound in air = 330 m s−1{}^{-1})

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Answer: (a)

  1. The siren approaches the cliff, so the cliff receives f1=f vv−uf_1 = f\,\dfrac{v}{v - u}.
  2. The stationary cliff reflects f1f_1 unchanged to the stationary observer.
  3. f1=800×330315≈838 Hzf_1 = 800 \times \dfrac{330}{315} \approx 838\text{ Hz}
  4. So the answer is (a) 838 Hz.
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