A sound wave of frequency `f` travels horizontally to the right . It is teflected from a larger vertical plane surface moving to left with a speed `v`. the speed of sound in medium is `c`
(a) The number of waves striking the surface per second is `f(c + upsilon)/(c)`
(b) The wavelength of reflected wave is `(c(c-upsilon))/(f(c+upsilon))`
(c) The frequency of the reflected wave is ` f((c+upsilon))/((c+upsilon))`
(d) The number of beats heard by a stationary listener to the left of the reflecting surface is `(upsilon f)/(c - upsilon)`

Options

A. The number of waves striking the surface per second is `((c+v))/cv`
B. The wavelength of reflected wave is `(c(c-u))/(v(c+u))`
C. The frequency of the reflected wave as observed by the stationary observer is `v((c+u))/((c-u))`
D. The number of beats heard by a stationary listener to the left of the reflecting surface is `(uv)/(c-u)`

Answer

D

Explanation

By the concept of doppler effect Apparent frequency (no. of wave) striking the wall `=upsilon=(C+u)/C upsilon`

frequency of reflected wave (wall become source) `upsilon''=(C+u)/(C-u) upsilon`
Apperent wavelength `C/(upsilon'')=(C(C-u))/(upsilon(C-u))`
So, option A,B,C are correct.