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Homework Help: Doppler Effect II (Both observer and source in motion)

  1. Jul 11, 2007 #1

    exi

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

    You're flying in an aircraft at 46 m/s. An eagle flies directly towards you at 11 m/s. Speeds are relative to ground.

    The eagle emits a cry at 3400 Hz, and the speed of sound is 330 m/s. What frequency do you hear?

    2. Relevant equations

    [tex]f_o = f_s\left( \frac{1\pm\frac{v_o}{v}}{1\mp\frac{v_s}{v}} \right)[/tex]

    Because the observer and source are both moving towards each other (presumably?),

    [tex]f_o = f_s\left( \frac{1+\frac{v_o}{v}}{1-\frac{v_s}{v}} \right)[/tex]

    3. The attempt at a solution

    Seems simple enough, but

    [tex]f_o = 3400\left( \frac{1+\frac{46}{330}}{1-\frac{11}{330}} \right)[/tex]

    Works out to 4902.8213 Hz, a wrong answer. This problem seemed straightforward, but I'm not sure what I'm missing.
     
    Last edited: Jul 11, 2007
  2. jcsd
  3. Jul 11, 2007 #2

    Dick

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    Check your math. That's not what I get.
     
  4. Jul 11, 2007 #3

    exi

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    Don't I feel silly, part 2.

    4007.5235 Hz. I've got only one remaining shot at that problem; I didn't make any other conceptual mistakes, correct?
     
  5. Jul 11, 2007 #4

    Dick

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    That's what I get, but I'm not claiming infallibility.
     
  6. Jul 11, 2007 #5

    exi

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    It's correct.

    Thanks much, sir; I'll just whistle and blame my calculator now.
     
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