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Help me out with this physics problem

  1. Apr 28, 2004 #1
    I have been scratching my head all night about this problem...

    A man standing close to an iron railing consisting of evenly-spaced uprights makes a sharp sound and hears a note of frequency 640hz. calculate the spacing between the uprights. (speed of sound in air = 330m/s)


    perhaps one of ya can help me out with this problem...


    THANKS!
     
  2. jcsd
  3. Apr 28, 2004 #2

    Integral

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    It is not clear to me that there is any relationship between the bars and the sound. But

    [Tex] \lambda = \frac v f [/tex]
    where
    [tex] \lambda= {Wavelength}[/tex]
    [tex] v= {velocity}[/tex]
    [tex] f = {frequency} [/tex]

    Is what you need.
     
  4. Apr 28, 2004 #3
    I get the problem. The sharp sound is a single discrete narrow pulse, and it echos of the bars, one after another, so that it's total return to the observer has the given frequency.

    To solve this problem, there is one more bit of information you'll need to know, and that's the speed of sound, which if I recall is about 770 mph at STP (convert that to m/s). Use that for v to get the bar spacing. Don't forget it's round trip time you'll be working with.

    I'm not 100% certain this is what the problem intends, so maybe you should desribe your assumptions in the answer to the homework problem. This way you can get credit even if the instructor intended something else.
     
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