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Physics · PYQ NEET UG 2016(1)
हिन्दीA siren emitting a sound of frequency \( 800\text{ Hz} \) moves away from an observer towards a cliff at a speed of \( 15\text{ ms}^{-1} \). Then, the frequency of sound that the observer hears in the echo reflected from the cliff is (Take velocity of sound in air \( = 330\text{ ms}^{-1} \))
Correct answer · Option 1
838 Hz
Explanation
Using the Doppler effect for source moving towards cliff: \( f' = f (\frac{v}{v - v_s}) = 800 (\frac{330}{330 - 15}) = 800 \times \frac{330}{315} \approx 838\text{ Hz} \).
