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Electric field problem! HELP.

  1. Jan 23, 2008 #1
    1. The problem statement, all variables and given/known data
    A tiny ball (mass = 0.014 kg) carries a charge of -17 C. What is the electric field magnitude that would cause the ball to float above the ground?


    2. Relevant equations
    what equation should I use? I am not sure how to even start this problem.

    3. The attempt at a solution
    Would using E = q/ ((E0 * A) be a good start?
     
  2. jcsd
  3. Jan 23, 2008 #2
    Not even that complicated, there's a ball with a mass m

    So there's a gravitational force acting downward on the ball that you should be able to find out

    You need to counter this gravitational force with another force caused by an electric field

    If you know the charge, you just need to find the electric field. What's the relationship between charge, electric field, and actual force?
     
  4. Jan 23, 2008 #3
    I think I got it... So i should use the E=F/q. And the force is the mass*acceleration which is gravity because it is directed downward.

    Thanks.
     
  5. Jan 23, 2008 #4
    Right

    so Fgrav=Felectric

    and Felectric=E*q
     
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