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In the figure shown a source of sound of frequency 510 Hz moves with constant velocity v_s=20m/s in the direction shown. The wind is blowing at a constant velocity of v_w=20m/s towards an observer who is at rest at point B. The frequency (in Hz) detected by the observer corresponding to the sound emitted by the source at initial position A will be (speed of sound relative to air = 330 m/s)
Option: 1
525

Option: 2
500

Option: 3
510

Option: 4
550

Answers (1)

best_answer

$\\ \text{The sound wave frequency is}\ \nu=510 \mathrm{Hz} \\ \text{The speed of sound relative to air is}, u=330 \mathrm{m} \mathrm{s}^{-1} \\ \text {Now, the apparent frequency of sound detected by observer is }\nu^{\prime}=\nu\left(\frac{u+v_{w}}{u+v_{w}-v_{s} \cos 60^{\circ}}\right) \\ \nu^{\prime}=510\left(\frac{330+20}{330+20-20 \cos 60^{\circ}}\right) \\ \nu^{\prime}=510\left(\frac{350}{340}\right)\\ \nu^{\prime}=525 H z$

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shivangi.bhatnagar

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