A driver in a stationary car blows a horn which produces monochromatic sound waves of frequency 1000 Hz normally towards a reflecting wall. The wall approaches the car with a speed of $6 m s^{- 1}$ : (Speed of sound in air is =330 m/s)

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The frequency of sound reflected from wall and heard by the driver nearly is 1037 Hz

The frequency of sound reflected from wall and heard by the driver nearly is 964 Hz

The percentage increase in frequency of sound after reflected from wall nearly is 3.7%

The percentage decrease in frequency of sound after reflected from wall nearly is 3.7%

answer is A, C.

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Detailed Solution

First by using Doppler's effect we can obtain the frequency of sound received by the wall considering it as a moving observer then we consider it as a moving source of this frequency and then we can find the frequency received by the driver as an observer. The analysis will result in option (A) and (C) correct.

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