A sound wave of frequency `f` travels horizontally to the right. It is reflected from a large vertical plane surface moving to left with a speed `v`. The speed of sound in medium is `C`

Options

A. The number of wave striking the surface per second is `f((c+v))/(c )`
B. The wavelength of reflected wave is `(c(c-v))/(f(c+v))`
C. The frequency of reflected wave is `(f(c+v))/(c-v)`
D. The number of beats heard by a stationary listener to the left to the reflecting surface is `(vf)/((c-v))`

Explanation

Number of waves encountered by the moving plane per unit time`=("distancetravelled")/("wave length")`
`=(c+v)/(lamda)=(c )/(lamda)(1+(v)/(c ))=f(1+(v)/(c ))`
`f'` is the frequency of the incident wave and `f''` is the frequency of the reflected wave that a stationary observer meets.
`f''=(f')/((1-(v)/(c )))=(f(1+(v)/(c )))/((1=(v)/(c )))=(f(c+v))/((c-v))`
`lamda''=(c )/(f'')=(c )/(f)((c-v)/(c+v))`
Beat frequency`=f''=f`
`=(f(1+(v)/(c )))/((1-(v)/(c )))-f=(2vf)/((c-v))`