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Charged Particles on a pendulum

  1. Feb 16, 2009 #1
    1. The problem statement, all variables and given/known data

    What is the distance(d) separating the charged particles dangling on the pendulum?

    Length of Nonconducting string=120cm
    mass of particles= 10g
    Charge q = 1.2*10^-8


    2. Relevant equations

    Fe=(k*q^2)/d^2



    3. The attempt at a solution

    I think I could get this problem easily if I had either the angle between verticle and the nonconducting string or the electric force opposing the masses. I have been using my knowledge of trigonometry to figure this out and trying to manipulate the above equation, but with no luck. Just needed to be pointed in the right direction I think. Thanks!
     
  2. jcsd
  3. Feb 16, 2009 #2

    Dick

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    Focus on one of the particles. You have three forces on the particle, gravity, electrical, and the tension force of the the string. They all have to balance (i.e. the sum is zero). Split each one of them into xy components and express them in terms of the unknown angle theta. Start writing down the equations you get, ok?
     
  4. Feb 16, 2009 #3
    ok.... I will show you what I have. I don't know Fe or Theta.....That is where I am hitting a roadblock. mg= .098N

    Fe=Tsin(theta)
    mg=Tcos(theta)
    Fe/mg=Tan(theta)

    Am I still overlooking something?
     
  5. Feb 16, 2009 #4

    Dick

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    You can also express Fe in terms of sin(theta), since the distance is a function of sin(theta).
     
    Last edited: Feb 16, 2009
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