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Finding combined amplitude of out of phase waves

  1. Aug 2, 2009 #1
    1. The problem statement, all variables and given/known data

    "Two waves are traveling in the same direction along a stretched string. The waves are 30.0° out of phase. Each wave has an amplitude of 4.00 cm. Find the amplitude of the resultant wave."

    2. Relevant equations

    y(x,t) = Asin(kx - [tex]\omega[/tex]t)

    3. The attempt at a solution

    Assuming that both waves are sinusoidal, I'm just summing up the two waves as follows:

    (4.00 cm)sin(kx-[tex]\omega[/tex]t) + (4.00 cm)sin(kx-[tex]\omega[/tex]t + 30)

    but I'm not sure how to find a numerical amplitude with this. Thanks for the help.
  2. jcsd
  3. Aug 2, 2009 #2


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    Science Advisor
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    Gold Member

    Look up the trig identity for sina + sinb.
  4. Aug 2, 2009 #3
    And don't forget to use radians to measure the angle, just to make things a bit more consistent.
    Last edited: Aug 2, 2009
  5. Aug 2, 2009 #4
    So what do I do with the variables "kx-[tex]\omega[/tex]t"? They're not given in the problem.
  6. Aug 2, 2009 #5
    You are only asked about the amplitude of the resultant wave. The rest is irrelevant.
  7. Aug 2, 2009 #6
    Ok thanks
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