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,

The number of waves striking the surface pre second is  $\frac{n(c+v)}{c}$

The frequency of the reflected wave is  $\frac{n(c+v)}{(c-v)}$

The wavelength of the reflected wave is  $\frac{c(c-v)}{n(c+v)}$

The number of beats heard by a stationary listener to the left of the reflecting surface is  $\frac{nv}{c-v}$