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Homework Help: Physics problem on force of a charge

  1. May 13, 2015 #1
    1. The problem statement, all variables and given/known data
    Two point charges are on the x-axis. One charge, q1 = +10nC, is located at the origin, and the other charge, p2=-18nC is located at x = 9.0m

    2. Relevant equations
    a.) what is the force on q2(include direction)?
    b.) what is the force on q1(include direction)?

    3. The attempt at a solution
    K = coulomb's law = 9.0*10^9
    I got 1.3122*10^14, but was told that was WAY wrong.
  2. jcsd
  3. May 13, 2015 #2


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    HI, Joshua. Welcome to PF!

    (1) Note that the charge is given in units of nC. You need to take into account the "n".
    It's a very good idea to include units in your calculation and make sure that the units combine to give the correct unit for the force.

    (2) Looks like you multiplied by 9^2 rather than divided by 9^2.

    (3) "k" is Coulomb's constant, not Coulomb's law.
  4. May 13, 2015 #3


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    I believe the "n" in "nC" stands for "nano".
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