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

A band music at a frequency f is moving towards a wall at a speedv_(b)

1.	A band music at a frequency f is moving towards a wall at a speedv_(b) . A motorist is following the band with a speedv_(m). If v is the speed of sound , obtain an expression for the beat frequency heard by the motorist .
Answer» SOLUTION :Two separate sounds will be heard by the motorist one is DIRECT from band and other is the echo the WALL . Apparent frequency of direct sound . `f_(1) = f ((V + v_(m))/(v+ v_(b))) ` Apparent frequency of the echo , `f_(2) = f ((v + v_(m))/(v+ v_(b))) ` Therefore , the beat frequency heard by the motorist, ` n= f_(2) - f_(1)= f(v + v_(m)). [(1)/(v - v_(b)) - (1)/(v+ v_(b))]` `= (2fv_(b) (v + v_(m)))/(v^(2)- v_(b)^(2))`