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Homework Help: Parallel plate capacitors

  1. Mar 23, 2010 #1
    1. The problem statement, all variables and given/known data

    The area of the plates of a parallel plate capacitor is 1 m2, the spacing between the plates is 10 cm, the potential difference between the plates is 1500 V. After beign charged, the plates are disonnected electrically from the surroundings. The plates are then pulled farther apart so that the new spacing is 11 cm.

    a. What is now the potential difference between the plates?
    b. How much work is required to pull the plates apart?
    c. Assume that the pulling apart of the plates is accomplished by a constant force of 10 N more than the force required to keep the plates apart. How fast are the plates moving away from one another when the plates are separated by 11 cm?

    2. Relevant equations


    3. The attempt at a solution

    The first parts are doable, if, like I'm assuming, the charge is going to be constant. However, without a mass given, I can't see how part c is going to work out. I figured it'd have something to do with energy conservation or kinematics, but I don't know how to solve for v without an m to put into the energy equation, or to figure the acceleration. Any help is appreciated.
  2. jcsd
  3. Mar 24, 2010 #2


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    Homework Helper

    You're right. You need the mass of the plates to answer the question.
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