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Homework Help: Doppler effect with 2 sound sources

  1. Sep 23, 2013 #1
    1. The problem statement, all variables and given/known data
    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.

    2. Relevant equations
    Doppler effect equation

    3. 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
    1. The problem statement, all variables and given/known data

    2. Relevant equations

    3. The attempt at a solution
  2. jcsd
  3. Sep 24, 2013 #2
    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..
  4. Sep 24, 2013 #3
    Thank you
  5. Sep 24, 2013 #4


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    Are you sure that's not 57kHz?
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