A sound wave of frequency `f` propagasing through air with a velocity `C`, is reflected from a surface which is moving away from the source with a constant speed `V`. Find the frequency of the reflected wave, measured by the observer at the position of the source.

Options

A. `(f (x - v ))/(c + v )`
B. `(f (c + v))/( c- v )`
C. `(f (c + 2 v))/( c + v )`
D. `(f (c - v ))/( c - 2v)`

Answer

A

Explanation

In first case observer (surface) is moving away. Perceived frequency
`f . = f (( c -v )/(c))`
In second case source (surface) is moving away. Perceived frequency
`f .. = f . ((c )/( c + v)) = f ((c -v )/( c + v ))`
Hence, frequency of the reflected wave is `=f (( c-v )/( c+ v))`