Sound WavesHardBloom L3
Question
A source is moving with constant speed vs = 20 m/sec towards a stationary observer due east of source. Wind is blowing at the speed of 20 m/sec due to 60° north of east. The source is generating of frequency 500 Hz. Then frequency registered by observer is: [Speed of sound in still air = 330 m/sec.]
Options
A.500 Hz
B.532 Hz
C.531 Hz
D.530 Hz
Solution
Sol. Along line joining source and observer
vs/w = 20 – 20 cos 60°
= 10 m/s
vo/w = – 20 cos 60° = – 10 m/s
f = $\left( \frac{330 + |v_{o/w}|}{330 - |v_{s/w}|} \right)f_{0}$ = $\left( \frac{330 + 10}{330 - 10} \right) \times 500$
= 531 Hz
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