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Homework Help: Electric fields problem

  1. Apr 2, 2009 #1
    An electric field causes the 5.0 g point charge to hang at a 20 angle. What is the charge of the ball

    I don't have the figure but it looks like a simple pendulum hanging at the angle of 20 degree
    1. The problem statement, all variables and given/known data
    E= 100,000 N/C
    m of the ball = 5g
    Angle =20 degree

    e0= 8.85*10^12

    2. Relevant equations

    E = F (electrostatic) on p / p (charge)

    F = (K q1 q2)/r12^2


    3. The attempt at a solution

    I have no clue
  2. jcsd
  3. Apr 2, 2009 #2


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    Homework Helper

    Draw a force diagram.

    Figure what needs to be in balance for the pendulum and weight to be at that angle.
  4. Apr 2, 2009 #3
    So basically, there will be tension, gravity and electric field act on it
    and gravity and electric field will have x,y component but how can we figure out Tension???
    So saying the ball doesn't move we can set everything =0 but we don't have tension
  5. Apr 2, 2009 #4
    Never mind, I've found the right answer....We actually don't need Tension to solve it
    Thanks for great hint
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