A car is moving towards a high cliff. The car driver sounds a horn of frequency `f`. The reflected sound heard by the driver has a frequency `2 f`. if v be the velocity of sound, then the velocity of the car, in the same velocity units, will be

Options

A. v/3
B. v/4
C. v/2
D. v/ 2

Answer

A

Explanation

According to given conditions

cliff is stationary source of freq. f' where
`f'=((v)/(v-v_"car"))f`
Freq. heard by the driver
`f''=((v+v_"car")/v)f'=((v+v_"car")/(v-v_"car"))f=2f`
`rArr v+v_"car"=2v-2v_"car" rArr 3v_"car" =v `
`rArr v_"car"=v//3`