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Homework Help: Ring charge propelling a sphere

  1. Mar 1, 2009 #1
    A 13.4 cm radius thin ring carries a uniformly distributed 14.8 microC charge. A small 8.2 g sphere with a charge of 2.4 microC is placed exactly at the center of the ring and given a very small push so it moves along the ring axis (+ x axis).

    How fast will the sphere be moving when it is 1.8 m from the center of the ring (ignore gravity)?

    I know i can treat the ring like a point charge so e=kq/r
    and (1/2)mv^2=e

    I just think I am doing everything after the e=kq/r step completely wrong. My last answer was 4248m/s.
  2. jcsd
  3. Mar 2, 2009 #2
    Treat the sphere as a point charge then determine the electric field produced by the ring as a function of x.
  4. Mar 2, 2009 #3


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    the symmetry of the ring along the x axis should greatly simplify things
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