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Homework Help: Frequency problem.

  1. Dec 6, 2007 #1
    1. The problem statement, all variables and given/known data

    Find the speed of a car if the tone of the horn drops by 36 percent as it passes you. The speed of sound is 340 m/s. Answer in units of km/h.

    2. Relevant equations


    solce for v source.

    3. The attempt at a solution

    I thought I would just set .36f = f (340/(340-x)) and solve for x (x= -604.4) this is not the right answer.
  2. jcsd
  3. Dec 6, 2007 #2
  4. Dec 7, 2007 #3

    Shooting Star

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    Homework Helper

    It drops by 36% in comparison to the frequency it had before passing you.

    The formula you've written above is incorrect, if it is for the moving away part.

    You have to consider both the source coming toward you initially and then receding.

    And, of course, the change in units, as mentioned in the last post.
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