A police car with a siren of frequency `8 KHz` is moving with uniform velocity `36 Km//hr` towards a ball building which reflects the sound waves. The speed of sound in air is `320 m//s`. The frequency of the siren heard by the car driver is

Options

A. `8.50kHz`
B. `8.25kHz`
C. `7.75kHz`
D. `7.50kHz`

Answer

A

Explanation

`f_("incident")=f_("reflected")=(320)/(320-10)xx8 kHz`
`f_("observed")=(320+10)/(320)=f_("reflected")=8xx(330)/(310)`
`8.51 kHz approx 8.5kHz`