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Homework Help: Waves on a string equation

  1. Jun 15, 2011 #1
    1. The problem statement, all variables and given/known data

    A wave on a string is described by the following equation: y = (15cm)cos(πx/5.0cm - πt/12s). Sketch this wave from x = 0 to x = 10 cm for the t = 0.

    3. The attempt at a solution
    Honestly, I've never seen this notation before. I have no idea how to interpret it. I tried googling some help and now I'm more confused. I tried setting t to 0 and putting different values for x in order to get a value for y, but I get 14.9... for every value of x, which gives me a straight line, and that answer was incorrect. It might be hard to explain this online, but I would appreciate it immensely if somebody would please try. I'm utterly lost.
  2. jcsd
  3. Jun 15, 2011 #2


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    Then you are doing something wrong in your calculations or choosing to few x's.
    For instance, if x = 0 then y = 15, if x = 2,5 then y = 0, if x = 5 then y = -15 and so on.
    How are you doing the calculations?
  4. Jun 15, 2011 #3
    This is what I am doing:

    Using x=2.5 for example,

    t=0, so...
    15 x cos[(pi*2.5)/5.0 - (pi*0)/12]
    15 x cos(1.57 - 0)
    15 x 0.9996 = 14.99

    I'm obviously doing something wrong, because I know for x=2.5 y should equal 0
  5. Jun 15, 2011 #4


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    your calculator is set to degrees, it should be set to radians.
  6. Jun 15, 2011 #5
    Omg...I feel like a complete moron.
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