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Homework Help: E and M help

  1. Jan 15, 2008 #1
    E and M help!!!

    I got 1.33x10^-6 for this question, can someone please verify/check it?

    "two charged balls are suspended on light 10cm strings. Each has a mass of 30g. In equilibrium, the total angle between the strings is 60 degrees. Assuming the balls are equally charged, what is the charge on each ball?"


  2. jcsd
  3. Jan 15, 2008 #2
    I'm assuming the balls would be right next to each other if hanging straight down?

    Did you
    A)Use trigonometry to figure out the distance between the balls at equilibrium?
    B)Use F=c*q^2/r^2 to figure out the force on the balls in terms of q?
    C)Use trig to figure out the force from gravity acting in the "swinging" direction on the balls?
    D)Use trig to figure out the electrical force(in terms of q still)acting against the "swinging" direction?
    E)Set those two equal and solve for q?

    What you probably did wrong, if you did something wrong(I didn't check the math)is do F=c*q^2/r^2 just like that, which is the force going in a straight line between the two, and set that equal to the gravitational force that's NOT going in a straight line between the two, and it's not gonna work
  4. Jan 15, 2008 #3


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    I think it would help us if you posted exactly what you did to get the answer you've stated angiecakes.
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