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Homework Help: Sound: freq moving sources

  1. Jun 28, 2003 #1


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    A train is traveling toward you at 120km/h. The train blows its 400Hz whistle. take the speed of sound to be 340m/s. whats the frequency do you hear?

    400/(1-(4.32x10^8 / 340)) i got 4.32x10^8 = 120000m * 3600sec

    what am i doing wrong?
    The possible answers are: which is it and what have i done wrong to miss this test question?

    a) 444hz
    b) 364hz
    c) 361 hz

    Dx :wink:
  2. jcsd
  3. Jun 28, 2003 #2

    Tom Mattson

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    You made a mistake converting the speed of the source from km/h to m/s. If you look at it, you have the source moving faster than light, which is a big no-no.
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