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 + u))/(c)v`
B. The wavelength of reflected wave is `(c(c - u))/(v(c + u))`
C. The frequency of the reflected wave as observed by the strationary observer is `v((c + u))/((c - u))`
D. The number of beats heard by a statiionary listener to the left of the reflecting surface is `(uv)/(c - u)`

Answer

A, B, C

Explanation

By the concept of dopplar effect Apperent 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`
Apparent wavelength `= (C)/(upsilon) = (C(C-u))/(upsilon(C + u))`
so option `A, B, C` are correct.