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Homework Help: Wave equation

  1. Dec 10, 2006 #1
    http://img208.imageshack.us/img208/8093/untitledrp9.png [Broken]

    i understand how the 'k' and 'w' values were calculated in the above problem. what i do not understand is why 134 s and 20.9m are being take to the -1 power. is the 20.9m being added because the problem states the wave travels in the -x direction? Thanks
    Last edited by a moderator: May 2, 2017
  2. jcsd
  3. Dec 10, 2006 #2


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    They are not. The -1 applies only to the units s and m respectively.
  4. Dec 10, 2006 #3
    That -1 is a dimensional thing, it is related to the units. In fact I think it's a bit unusual to keep the units in midway through a calculation, it would have been better to bulk them together at the end, but don't let it confuse you!

    Mathematically A-x=1/Ax

    It's just a notational thing, you'll note that it lets you do that rule where you can just add the powers when you're multiplying things together.

    e.g. A2*A-1=A2/A=A

    so basically: m/s=ms-1
    and: 1/s=s-1
  5. Dec 10, 2006 #4


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    Omitting units is a shortcut; if you want to write true statements, you have to carry the units throughout the equation. (And being careful with the units can prevent a good number of mistakes too)
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