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Homework Help: Doppler/Beats question

  1. Jan 31, 2008 #1
    1. The problem statement, all variables and given/known data
    A bat emits a sound at a frequency of 37.0 kHz as it approaches a wall. The bat detects beats with a frequency of 832 Hz between the sound it emits and the echo bouncing from the wall. What is the speed of the bat? (The speed of sound is 335 m/s.)

    2. Relevant equations
    f_beat = |f1 - f2|
    f1 = (1/1-vbat/v)f When the Bat is the source approaching the wall
    f2 = (1+vbat/v)f1 When the Bat is the observer and the sound is echoed off the wall

    3. The attempt at a solution
    832 = |f1 - f2|
    f1 = 832+f2
    So essentially i have two equations, two unknowns
    832+f2 = (1/1-vbat/335)37000
    f2 = (1+vbat/335)832+f2
    Worked to isolate f2 in both equations and equated them together, now this seems to be way too much work... numbers were huge and even when i worked it through the answer was wrong, What is wrong with my approach?
  2. jcsd
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