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Homework Help: Two Electric Charges- Electric Force-Ranking

  1. Dec 3, 2011 #1
    1. The problem statement, all variables and given/known data
    Below are seven arrangements of two electric charges. All of the charges are the same size, 20 C, but they are either positive or negative. Each figure also has a point labeled P that lies on a straight line with the two charges. The distance between any two items is all 5 cm. There are no other charges in this region. A +5 C charge is placed at point P. Rank the strength (magnitude only) of the electric force on the +5 C charge when it is placed at point P from greatest to least.


    2. Relevant equations
    Fe= k(q1q2)/r^2

    3. The attempt at a solution
    help get me started please? :) I don't know how to get started.
    Last edited: Dec 3, 2011
  2. jcsd
  3. Dec 3, 2011 #2


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    What do you mean by that? Is 5 cm the distance from P of both the + and - charges?

  4. Dec 3, 2011 #3
    between any two items is 5 cm. For example, in C,
    between - and P it is 5 cm and between P and + it is 5 cm.
  5. Dec 3, 2011 #4


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    And what is the distance between + and - in B?
    Anyway, the + and - charges are of the same in magnitude, so what about the force they exert on the charge at P if the distances are equal? What about the direction the forces? Draw the forces with arrows in the pictures, and determine the resultant.

  6. Dec 3, 2011 #5
    Oh! I think I understand it now. Thank you
  7. Dec 3, 2011 #6


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    Hi jeandempsey. Welcome to PF.

    Would you like to give your answers & your reasoning so that ehild or one of our other homework helpers can check that you really do understand this.
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