A band playing music at a frequency `f` is moving towards a wall at a speed `v_(b)`. A motorist is following the band with a speed `v_(m)`. If `v` is the speed of sound, obtain an expression for the beat frequency heard by the motorist.

Options

A. ` (v + v_(m))/(v + b_(b)) f`
B. ` (v + v_(m))/(v - b_(b)) f`
C. `(2 v_(b) (v + v_(m)))/(v^(2) - v_(b)^(2))f`
D. `(2 v_(m) (v + v_(b)))/(v^(2) - v_(m)^(2))`f

Answer

C