Question

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

• A. The number of waves striking the surface pre second is $\frac{n(c+v)}{c}$.
• B. The frequency of the reflected wave is $\frac{n(c+v)}{(c-v)}$.
• C. The wavelength of the reflected wave is $\frac{c(c-v)}{n(c+v)}$.
• D. The number of beats heard by a stationary listener to the left of the reflecting surface is $\frac{nv)}{c-v}$.

Answer 1

Answer: (A), (B), (C)

The correct options are
A The number of waves striking the surface pre second is $\frac{n(c+v)}{c}$.
B The frequency of the reflected wave is $\frac{n(c+v)}{(c-v)}$.
C The wavelength of the reflected wave is $\frac{c(c-v)}{n(c+v)}$.

apparent frequency of wave with freq n

$f_1=\frac{c+v}{c}n$

for reflected wave apparent frequency will be

$f_2=\frac{c}{c-v}{f}_1=n\frac{c+v}{c-v}$

wavelength $\lambda =\frac{c}{f}=\frac{c}{f_2}=\frac{c(c-v)}{n(c+v)}$