A source of sound of frequency `256Hz` is moving rapidly towards wall with a velocity of `5m//sec`. How many beats per second will be heard if sound travels at a speed of `330m//sec`.

Explanation

NOTE : If the sound reaches the observer after being reflected from a stationary surface and the medium is also stationary, the image of the source in the reflected surface will become the source of the reflected sound.
`v' = v[(c - v_(0))/(c - v_(s))]`
`v_(0)`, `v_(s)` are `+ve` if they are directed from source to the observer and `-ve` if they are directed from observer to source.
`v' = 256[(330 - (-5))/(330 - 5)] = 264 Hz`
:. Beat frequency `= 264 - 256 = 8`