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

Answer

3

Explanation

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