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High speed train sounding horn - Doppler effect

  1. Nov 10, 2007 #1
    A high speed train is traveling at a speed of 41 m/s when the engineer sounds the 416 Hz warning horn. The speed of sound is 345 m/s. What is the frequency of the sound as perceived by a person standing on at the crossing when the train is leaving?

    I used the equation: f0=fs/(1-vs/v)
    f0=416 Hz / 1-(41 m/s / 345 m/s)
    f0=366.6

    I'm not sure what I'm doing wrong... =(
     
  2. jcsd
  3. Nov 10, 2007 #2

    G01

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    You want to find the observed frequency for when the train is moving away from the observer. When the source is moving away from the observer, the sign in the denominator is positive, not negative. That is you problem.
     
  4. Nov 11, 2007 #3
    oh okay thanks!
     
  5. Nov 11, 2007 #4

    G01

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    No problem. :smile:
     
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