The driver of a car travelling with a speed of 30 m/s towards a wall sounds a siren of frequency 500 Hz. If the velocity of sound in air is 330 m/s, then the frequency of the sound reflected from the wall and as heard by the driver is

Options

A. 550 Hz
B. 600 Hz
C. 650 Hz
D. 450 Hz

Answer

B

Explanation

For the source moving towards the wall,
`n_(A_(1)) = (V)/(V - V_(s)) xx n`
`= (330)/(330 - 30) xx 500 = 550 Hz`
For the reflected sound waves, the dirver acts as an observer moving towards the wall
`:. n_(A_(2)) = (V + V_(0))/(V) = xx n_(A_(1))`
`= (330 + 30)/(330) xx 550 = 600 Hz`