Sound WavesHardBloom L3

Question

The difference between the apparent frequencies of a sound source as perceived by a stationary observer during its approach and recession is 2% of the actual frequency of the source. The speed of source is (Speed of sound = 300 m/s)

Options

A.3 m/s
B.1.5 m/s
C.10 m/s
D.6 m/s

Solution

Sol. f1 = $\left( \frac{v}{v - v_{s}} \right)f_{0}$

f2 = $\left( \frac{v}{v + v_{s}} \right)f_{0}$

$\frac{f_{1} - f_{2}}{f_{0}}$ = 2% = $\left( \frac{v}{v - v_{s}} - \frac{v}{v + v_{s}} \right)$

⇒ $\frac{2}{100} = \left( \frac{2vv_{s}}{v^{2} - v_{s}^{2}} \right)$

⇒ $\frac{2}{100} = \frac{2 \times 300v_{s}}{(300)^{2} - v_{s}^{2}}$

⇒ $v_{s} \cong 3m/s$

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