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

Answer

A, B, C

Explanation

Moving plane is like a moving observer. Therefore, number of waves encountered by moving plane
`f_(1)=f((v+v_(0))/(v))=f((c+v)/(c))`
Frequency of reflected wave,
`f_(2)=f_(1)((v)/(v-v_(s)))=f((c+v)/(c-v))`
Wavelength of reflected wave,
`lamda_(2)=(v)/(f_(2))=(c)/(f_(2))=(c)/(f)((c-v)/(c+v))`
Number of beats heard `= f_(2) -f = (2 vf)/(c - v)`.