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)`

Explanation

Moving plane is like a moving observer. Therefore , number of waves encountered by moving plane,
`f_(1)= f((upsilon + upsilon_(0))/(upsilon))= ((c + upsilon)/(c - upsilon))`
frequency of reflected wave, `f_(2) = f_(1) ((upsilon)/(upsilon - upsilon_(s)))= f((c - upsilon)/(c + upsilon))`
Wavelength of reflected wave, `lambda_(2)=(c) /(f_(2))= (c)/(f)((c- upsilon)/(c + upsilon))`
Beat frequency , `f_(b)= f_(2) - f= f((c + upsilon)/(c - upsilon))- f= (2 fupsilon)/(c-upsilon)`
Therefore, the correct options are (a), (b) and(c ).