Question

# When a source moves away from a stationary observer, the frequency is $$6/7$$ times the original frequency. Given: speed of sound = $$330\,m/s$$ . The speed of the source is

A
$$40\,m/s$$
B
$$55 \,m/s$$
C
$$330\,m/s$$
D
$$165 \,m/s$$
Solution
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#### Correct option is B. $$55 \,m/s$$$$\nu' = \dfrac{\nu}{\nu + \nu,}\nu$$ or $$\dfrac{6}{7} \nu = \dfrac{330}{330 + \nu,}\nu$$ or $$6 \times 330 + 6 \nu, = 7 \times 330$$ or $$6 \nu, = 330$$ or $$\nu, = 55\,m/s$$

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