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

Options

A. `(v)/(l)`
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)`.