A driver in a stationary car blows a horn which produces monochromatic sound waves of freqeuncy 1000 Hz normally towards a reflecting wall. The wall approaches the car with a speed of `3.3(m)/(s)`.

Options

A. The frequency ofsound reflected from wall and heard by the driver is 1020 Hz
B. The frequency ofsound reflected from wall and heard by the driver is 980 Hz
C. The percentage increase in frequency of sound after reflected from wall is 2%
D. The percentage decrease in frequency of sound after reflected from wall is 2%

Answer

A, C

Explanation

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