A siren emitting a sound of frequency 800 , H | vedclass

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(B) The frequency of the sound emitted by the siren is $f_0 = 800 \, Hz$.The speed of the source (siren) is $v_s = 15 \, m s^{-1}$.The speed of sound

Vedclass · Accepted Answer

$838$

Vedclass · Answer

(B) The frequency of the sound emitted by the siren is $f_0 = 800 \, Hz$.The speed of the source (siren) is $v_s = 15 \, m s^{-1}$.The speed of sound in air is $v = 330 \, m s^{-1}$.Since the siren is moving towards the cliff,the cliff acts as an observer receiving the sound. The frequency $f'$ received by the cliff is given by the Doppler effect formula for a moving source and stationary observer:$f' = f_0 \left( \frac{v}{v - v_s} \right) = 800 \left( \frac{330}{330 - 15} \right) = 800 \left( \frac{330}{315} \right) \approx 838.09 \, Hz$.The cliff reflects this sound back to the original observer. Since the cliff is stationary,it acts as a stationary source emitting sound at frequency $f'$. The original observer is stationary relative to the cliff,so they hear the reflected sound at the same frequency $f'$.Therefore,the frequency heard by the observer is approximately $838 \, Hz$.

$A$ siren emitting a sound of frequency $800 \, Hz$ moves away from an observer towards a cliff at a speed of $15 \, m s^{-1}$. The frequency of sound that the observer hears in the echo reflected from the cliff is .... $Hz$ (Take velocity of sound in air $= 330 \, m s^{-1}$)

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