Question

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:-

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

Answer 1

The correct option is C The frequency of the reflected wave is $f\frac{(c+v)}{(c-v)}$

frequency of the waves striking =$n^1$ = $\frac{(c+v)}{\lambda }$ =$\frac{f(c+v)}{c}$

frequency of the waves reflecting =$n^2$ =($\frac{c}{c-v})n^1$

$n^2$ = $f\left(\frac{c+v}{c-v}\right)$