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Homework Help: Frequency physics homework

  1. Nov 23, 2004 #1
    A man standing by a rail track, hears the whistle of a train at a frequency of 10419.7 Hertz. The train is moving towards the man at a speed of 39.9 meters/sec. The frequency of the whistle (in Hertz) is

    Student response 9207.612
    Correct answer 9164.147

    frequency heard by the man = [1/(1-[u/v])} * frequency of whistle
    u=39.9 m/s
    v=343 m/s
    frequency heard by the man=10419.7
    so, the frequency of the whistle is 9207.612 but the correct answer is 9164.147
    What did I do wrong? please help, thanks.
  2. jcsd
  3. Nov 24, 2004 #2

    Andrew Mason

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    Science Advisor
    Homework Helper

    You are right if the speed of sound is 343 m/sec. That assumes temperature of 20 degrees C. If the temperature is 0 degrees C, the speed is 331.4 m/sec which results in factual = 9165 m/sec. What does the problem give for the speed of sound or temperature?

  4. Nov 24, 2004 #3
    It does not give the temperature nor speed of sound.
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