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. 8.5 hz
B. 8.25 kHz
C. 7.25 kHz
D. 7.5 kHz

Answer

A

Explanation

`36km^(-1)=36xx5/18`
`=10ms^(-1)`

Apart frequency of sound heard by are driver (observer)
`f..=f((v+v_(0))/(v-v_(s)))`
`=8((320+10)/(320-10))`
`f..=8.5kHz`