# Doppler effect with 2 sound sources

## Homework Statement

A fly is moving with a speed vl=3m/s and a bat is chasing it with vs=5m/s. The bat is emitting a sound with fs=50kHz. They are moving on the same line towards point C which is a source emitting a sound at f'=57Hz. Find the frequency of the total sound the fly is hearing. The fly has a length of 2mm.

## Homework Equations

Doppler effect equation

## The Attempt at a Solution

The fly is hearing from the bat a sound at a frequency f1=(v-vl)*fs/(v+vs)=50.3kHz approximately
The fly is also hearing a sound from source C f2=(v+vl)*f'/v=57.5Hz
where v=343m/s speed of sound
The frequency of the sound the bat is emitting is not influenced by source C and vice versa.
Since f1>>f2 the fly will hear two different sounds with discrete frequency
The length of the fly i assume that it is not needed in the calculations

## The Attempt at a Solution

Hi,
Since the bat is moving towards the fly, in the equation for f1 the denominator should be (v-vs). Other than that everything is OK..

Thank you

haruspex