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Homework Help: Car physics Sound Problem

  1. Sep 22, 2005 #1
    I am having a problem with the following question.

    A car is moving at 30 m/s. The cars horn is emmitting a 220 hz sound. The speed of sound is 343 m/s. How far does the the car move in one period of the sound emitted from the horn.

    I am having a problem determining the distance formula.
    The period of the 220 hz sound is 1/220hz = 4.54 ms

    so in 4.54 ms the sound has travelled 1.55722 meters (343 * .00454)

    Now the distance the car travels would be (4.54 ms * 30 m/s) = .1362 meters

    Is this the correct way to go about this problem?
  2. jcsd
  3. Sep 22, 2005 #2

    Andrew Mason

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    Science Advisor
    Homework Helper

    Yes. 1.557 meters is the wavelength of the sound: [itex]\lambda = v/f[/itex]. The apparent wavelength depends on where the observer is. If the observer is behind the car, the wavelength appears to be 1.557+.1362. If the observer is in front, it is .1557 - .1362.

  4. Sep 22, 2005 #3

    I thought I was correct in my calculations.
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