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Homework Help: Charges in a Line Conceptual Question with picture

  1. Sep 11, 2012 #1
    1. The problem statement, all variables and given/known data

    Two balls, one with charge Q1 = +Q and the
    other with charge Q2 = +2Q, are held fixed at a
    separation d = 3R as shown.

    See picture.

    Another ball with (non-zero) charge Q3 is
    introduced in between Q1 and Q2 at a
    distance = R from Q1.

    See right below first picture.

    • Which of the following statements is correct?

    1. The force on Q3 can be zero if
    Q3 is positive
    2. The force on Q3 can be zero if
    Q3 is negative
    3. The force on Q3 can never be
    zero, no matter what the (nonzero)
    charge Q3 is.

    2. Relevant equations

    F = kq1q2/r

    3. The attempt at a solution

    I initially said two but then changed my mind because the +2Q charge will always exert a force on Q3 (although it may not be as strong). What do you all think?

    Attached Files:

  2. jcsd
  3. Sep 11, 2012 #2
    Find the net force in each case on charge Q3.
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