A band playing music at a frequency `f_(0)` is moving towareds a wall at a speed `v_(0)`. A motorist is following the band with a speed `v_(m)`. If v be the speed of the sound the expression for beat frequency heard by motorist is

Options

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

Answer

C

Explanation

`upsilon_("direct")=upsilon[(V+v_(m))/(V+v_(b))]`, `upsilon._("reflected")=upsilon[(V+v_(m))/(V-v_(m))[`
beats/s`=upsilon_(2)-upsilon_(1)`