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

Answer

A, C

Explanation

`f'=f((v+v_(wall))/(v-v_(wall)))`
`f'=1000((340+3.3)/(340-3.3))=1020Hz`
`(f'-f)/(f)xx100=(trianglef)/(f)xx100=2%`