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Homework Help: Ok, how should I go about this one?

  1. Jan 18, 2006 #1
    Pendulum

    A small 12.00g plastic ball is suspended by a string in a uniform, horizontal electric field with a magnitude of 10^3 N/C. If the ball is in equilibrium when the string makes a 30 ° angle with the vertical, what is the net charge on the ball?

    Q = _________ C

    I know Coloumb's Law, and I assume I want to implement it here somehow, however I don't know where to begin on setting this one up.
     
  2. jcsd
  3. Jan 18, 2006 #2
    Oh, and here is the visual.
     

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  4. Jan 18, 2006 #3

    Doc Al

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    Staff: Mentor

    The ball is in equilibrium. What does that tell you?
     
  5. Jan 18, 2006 #4
    That there is no force acting on it?
     
  6. Jan 18, 2006 #5
    No, that isn't exactly the definition of equilibrium.

    Equilibrium is when there is no _net_ force acting on it.
     
  7. Jan 18, 2006 #6

    Doc Al

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    Staff: Mentor

    That there's no net force acting on it. Or, in other words: The net force is zero.

    Start by identifying all the forces acting on the ball, then set up the equations for equilibrium. (Analyze the x and y components separately.)
     
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