A car moving with a speed of 72 km-hour $^{- 1}$ towards a roadside source that emits sound at a frequency of 850 Hz. The car driver listens to the sound while approaching the source and again while moving away from the source after crossing it. If the velocity of sound is 340 $m s^{- 1}$ ,the difference of the two frequencies, the driver hears is

50 Hz

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85 Hz

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100 Hz

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150 Hz

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Solution

The correct option is C 100 Hz
The speed of the car is $72 k m / h = 20 m / s$
The frequency of source while approaching the source= $f_{0} (\frac{340 + 20}{340})$
The frequency of source while moving away from the source= $f_{0} (\frac{340 - 20}{340})$
Hence the difference in the observed frequencies= $\frac{40}{340} f_{0} = 100 H z$

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Similar questions

Q. A car is moving with a speed of

72 k m h^{- 1}

towards a roadside source that emits sound at a frequency of

850 H z

. The car driver listens to the sound while approaching the source and again while moving away from the source after crossing it. If the velocity of sound is

340 {m s}^{- 1}

, the difference of the two frequencies, the driver hears is:

Q. A source and listener are moving towards each other with the speed of 54 km/hr. If the true frequency of sound emitted by the source is

500 H z

, calculate the observed frequency when both source and listener are moving towards each other. Velocity of sound in air =

330 m s^{- 1}

A stationary source emits sound of frequency $f_{0} = 492 H z$ . The sound is reflected by a large car approaching the source with a speed of $2 m s^{- 1}$ . The reflected signal is received by the source and superposed with the original. The beat frequency of the resulting signal is $H z$ . (Given that the speed of sound in air is $330 m s^{- 1}$ and the car reflects the sound at the frequency it has received).