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Homework Help: Electricity, force, and component form

  1. Jan 9, 2007 #1
    1. The problem statement, all variables and given/known data

    Consider the four charges in Figure P25.46 http://i137.photobucket.com/albums/q208/infinitbelt/p25-46.gif [Broken] , in which d = 3 cm, q = 4 nC, the +x-axis points to the right, and the +y-axis points up. What is the force on the 1 nC charge at the bottom? Give your answer in component form, using i and j for and , respectively.

    2. Relevant equations

    F 2on1 = (K|q1||q2|)/r^2
    F 3on1 = (K|q1||q3|)/r^2

    3. The attempt at a solution

    I did for force 2 on 1 :[(9 x 10^9)(5 x 10^-9)(8 x 10^-9)]/(sqrt(0.03^2 + 0.048^2))^2
    Then I did tan(theta) = 4.8/3.0 = 57.994 degrees

    1.12 x 10^-4 N * sin(57.994) = 9.5 x 10^-5 N

    Then for the other force 3 on 1: [(9 x 10^9)(5 x 10^-9)(5 x 10^-9)]/0.03^2 = 2.5 x 10^-4 N

    I am confused as to what to do from here. Any ideas?

    Last edited by a moderator: May 2, 2017
  2. jcsd
  3. Jan 10, 2007 #2
    I'm not sure I follow your method. I know that the force on a charge due to another charge is [tex] F= \frac{kQq}{r^2}[/tex] where k is approximately [tex]9x10^9 N M^2 C^{-2}[/tex].

    I'm not sure of your reasoning for plugging in 8nC or 5nC into the equation. You are also talking about q1 and q3; I don't know what those are because they aren't labeled on your diagram. Please explain your reasoning for reach step.
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