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Question: Answered & Verified by Expert
An engine moving away from a vertical cliff blows a born at a frequency f. Its speed is $0.5 \%$ of the speed of sound in air. The frequency of the reflected sound received at the engine is
PhysicsWaves and SoundKVPYKVPY 2013 (SB/SX)
Options:
  • A $0.990 \mathrm{f}$
  • B $0.995 \mathrm{f}$
  • C $1.005 \mathrm{f}$
  • D $1.010 \mathrm{f}$
Solution:
2929 Upvotes Verified Answer
The correct answer is: $0.990 \mathrm{f}$
$f_{1}=f_{0}\left[\frac{v}{v+v_{s}}\right]$
$f_{R}=f_{1}\left[\frac{v-v_{s}}{v}\right]=f_{0}\left[\frac{v-v_{s}}{v+v_{s}}\right]=\left[1-\frac{2 v_{s}}{v}\right] f$
$=0.990 f$

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