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Finding theta for Coloumb's law suspension

  1. Jan 27, 2015 #1
    1. The problem statement, all variables and given/known data
    Two spheres are suspended on strings and repel each other. Using the graphing function of your calculator setup and solve a formula to find theta.

    The length of the rope is 3.0m, q = 1.0e4 and m = .2 kg.

    2. Relevant equations
    F=k*q1*q2/r^2

    3. The attempt at a solution
    Using newton's second law I've tried several times to set up the formula to solve for theta but I am unable.

    I know that the y component of tensions is equal to the force of gravity. Also that the X component of tension is equal to force caused by the repulsion of the two charges.
     

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    Last edited: Jan 27, 2015
  2. jcsd
  3. Jan 27, 2015 #2

    BvU

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    Equations look OK to me. Perhaps the instruction means they want you to solve numerically, not analytically ?
     
  4. Jan 27, 2015 #3
    We were told to find the equation, set it equal to zero and plug in our given mass, charge and length then find the x intercept with a graphing calucator. I get 60 degrees which is about twice what it should be.
     
  5. Jan 27, 2015 #4

    BvU

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    Can't find any givens under
    1. The problem statement, all variables and given/known data
    Perhaps you can use this thread to check if your calculator works properly

    (Although I admit that for the numbers at the bottom of your sheet ##\pi/3## fits a lot better than ##\pi/6## :) )
     
  6. Jan 27, 2015 #5
    Oops, that's what I get for being in a rush. The length of the rope is 3.0m, q = 1.0e4 and m = .2 kg.
     
  7. Jan 27, 2015 #6

    BvU

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    Hefty charge !
     
  8. Jan 27, 2015 #7
    Oh jeeze I just cannot type tonight. q = 1.0e-4
     
  9. Jan 27, 2015 #8

    BvU

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    Well, as I said,
    So I'm at a loss. How do you know that it's not right ?

    (can always try the check with this other thread to see if that fits...)
     
  10. Jan 27, 2015 #9
    My professor said that the angle should be about 30 degrees. It's possible I misheard though. I can't find an error so I think that might be the case.
     
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