Sound of frequency 1000 Hz from a stationary source is reflected from an object approaching the source at $30 m s^{- 1}$ , back to a stationary observer located at the source.The speed of sound in air is $330 m s^{- 1}$ .The frequency of the sound heard by the observer is

1200 H z

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1000 H z

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1090 H z

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1100 H z

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Solution

The correct option is A $1200 H z$
Frequency recieved by approaching car
$f_{1} = f_{0} (1 + \frac{30}{330}) H z$
where $f_{0} = 1000 H z$
$f_{1} = 1000 (1 + \frac{1}{11}) H z$
Frequency recieved by source again
$f_{2} = \frac{f_{1}}{1 - \frac{30}{330}} = \frac{1000 (1 + \frac{1}{11})}{1 - \frac{1}{11}} = 1200 H z$

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Sound of frequency 1000 Hz from a stationary source is reflected from an object approaching the source at 30ms−1, back to a stationary observer located at the source.The speed of sound in air is 330ms−1.The frequency of the sound heard by the observer is

The correct option is A 1200HzFrequency recieved by approaching carf1=f0(1+30330)Hzwhere f0=1000Hzf1=1000(1+111)HzFrequency recieved by source againf2=f11−30330=1000(1+111)1−111=1200Hz

Sound of frequency 1000 Hz from a stationary source is reflected from an object approaching the source at $30 m s^{- 1}$ , back to a stationary observer located at the source.The speed of sound in air is $330 m s^{- 1}$ .The frequency of the sound heard by the observer is