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Homework Help: Electrostatics - Question about the direction of the force.

  1. May 26, 2010 #1
    1. The problem statement, all variables and given/known data

    Two point charges, q1 = -2nC & q2 = +5nC are 4 cm apart. What is the force on q1? What is the force on q2? (Magnitude and Direction)

    2. Relevant equations

    F = kq/r^2
    k = 9x10^9

    3. The attempt at a solution

    Using that formula, I calculated q1 to equal -45kN and q2 to equal 112.5 kN (Which seems awfully large to me). I don't understand what the question needs in terms of a direction. It would make more sense to me if there were a set of coordinate related to the question.

    Any help appreciated,
  2. jcsd
  3. May 26, 2010 #2


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    Science Advisor
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    Gold Member

    If you show exactly what numbers you put where, we might be able to find out where you went wrong.

    As far as the direction is concerned, does the force on q1 point towards q2 or away from q2? What the force on q2?

    As far as the magnitudes of the forces are concerned, you need to brush up on Newton's Third Law.
  4. May 26, 2010 #3
    the formula for electrostatic force is k*q1*q2/r^2 be careful about the units
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