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A band playing music at a frequency v is...

A band playing music at a frequency v 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, the expression for the beat frequency heard by the motorist is

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The correct Answer is:
`(2fv_(b)(v+v_(m)))/((v^(2)-v_(b)^(2)))`
Frequency reaching the wall `f_(1)=f_(0)((v)/(v-v_(b)))`
Frequency reaching the motorist after reflection from wall
`f_(1)=f_(1)((v+v_(m))/(v))=f_(0)((v+v_(m))/(v-v_(b)))`
Frequency directly reaching the motorist
`f_(2)=f_(0)((v+v_(m))/(v+v_(b)))`
`:.` Beat frequency
`Deltaf=f_(1)-f_(2)=f_(0)(v+v_(m))((2v)/(v^(2)-v_(b)^(2)))`
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