Question

A sound source $A$ and a reflecting surface $B$ move directly toward each other.
Relative to the air, the speed of source $A$ is $29.9m/s,$ the speed of surface $B$ is $65.8m/s,$ and the speed of sound is $329m/s$.
The source emits waves at frequency $1200Hz$ as measured in the source frame.
In the reflector frame, what is the frequency of the arriving sound waves?

Answer 1

We know , $f=1200Hz$ and $v=329m/s$

(a) In this case, $v_D=65.8m/s$ and

$v_S=29.9m/s$, and we choose signs so that

$f^{\prime }$ is larger than $f$

$f^{\prime }=f\left(\frac{329m/s+65.8m/s}{329m/s-29.9m/s}\right)=1.58\times {10}^{3}Hz$