Question

A car is approching a railway crossing at a speed of `72 kmph`. It sounds a horn, when it is `800 m` away, at `600 Hz`. If the velocity of sound in air is `330 ms^(-1)`. The apparent frequency as received by a man at rest near the railway track perpendicular to the road at a distance of `600 m` from the crossing the

A. `653 Hz`
B. `365.5 Hz`
C. `630.5 Hz`
D. `563.5 Hz`

Answer 1

Correct Answer - C
`f = f_(0)"(v_(sound))/(v_(sound) - v_(source))`
`= 600 .(330)/(330 - vcostheta)`
`= 600 (330)/(330 - 20 cos37)`
`= 600.((330)/(314)) = 630.5 Hz`.