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Homework Help: Dopler effect question

  1. Aug 19, 2010 #1
    A bat is chasing an insect. if the bat, moving at 6m/s emits a 40kHz sound and recieves back an echo at 40.4 kHz. What speed and direction is the insect moving? take the speed of sound to be 343m/s

    Okay sooo.
    ive mucked around with this a fair bit

    so i know before f'>f that, so the insect is moving towards the bat

    f' = f( (v + Vd) / (v- Vs) )
    so the bat is both the source and detector
    i tried to write it in terms of the insect
    so Vd = Vb - Vi
    and Vs = Vb - Vi

    so i get Vi = f( V + Vb) + f' ( -v + Vb) all over f + f '
    which = 4.29 m/s
    is that correct?
    Last edited: Aug 19, 2010
  2. jcsd
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