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)`

Answer

A

Explanation

Number of pulse encountered by the moving plane per unit time is given by
`v'=("distance travelled")/("wavelength")=(C+V)/(lamda)=(C)/(lamda)(1+(V)/(C))=V(1+(V)/(C))`
Frequency of reflected pulses, received by an observer on graound `V"=(C)/(C-V)V'=((C+V)/(C-V))V`
Reflected wavelength`=(C)/(V")=(C)/(V)((C-V)/(C+V))`
Beats `v"-v((C+V)/(C-V))-v=(2vV)/(C-V)`.