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Homework Help: Charged particle suspended from elastic cord

  1. Sep 5, 2011 #1
    1. The problem statement, all variables and given/known data

    A charged particle with mass m = 200g and charge q = 25 µC is suspended from an elastic cord with force constant K = 5 N/m in a vertically upward electric field E of magnitude 3.7 x 10^5 N/C. What is extension of the cord when the particle is in equilibrium?

    2. Relevant equations

    3. The attempt at a solution
  2. jcsd
  3. Sep 6, 2011 #2

    first draw a free body diagram. there are three forces acting on the body. [itex]mg[/itex] downwards , the force of restoration due to the elastic cord , according to Hook's law is
    [itex]kx[/itex] upward and the force due to electric field [itex]F_e[/itex] upward. when in equilibrium, they balance.

    [tex]F_e+kx = mg[/tex]

    solve for x, the extension.
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