Question

A source of sound of frequency $256Hz$ is moving rapidly towards a wall with a velocity of $5m/s$. How many beats per second will be heard by the observer on source it self if sound travels at a speed of $330m/s$?

Answer 1

The observer will hear two sound, one directly from the source and other from reflected image of sound.

Hence number of beats heard per seconds

$\left(\frac{V}{V-V_s}\right)n-\left(\frac{V}{V+V_s}\right)n$

$\frac{2nV{V}_s}{V^2-V_s^2}=\frac{2\times 256\times 330\times 5}{335\times 325}=7.8Hz$