A wall is moving with constant velocity `u` towards a fixed source of sound of frequency `f`. The velocity of sound is `v`. The wavelength of the sound reflected by the wall is

Options

A. `(v)/(f)`
B. `(v-u)/(f)`
C. `(v+u)/(f)`
D. `(v-u)/(v+u).(v)/(f)`

Answer

D

Explanation

Frequency of sound reflected by wall `f'=(v+u)/(v)f`
Wavelength of sound reflected by wall
`=(v-u)/(f')=(v-u)/(v+u)xx(v)/(f)`.