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Homework Help: Electric Force between glass ball and rubber ball

  1. May 22, 2008 #1
    1. The problem statement, all variables and given/known data

    What is the electric force between a glass ball with 3.5 µC of charge and a rubber ball with -5.0 µC of charge when they are separated by 5 cm?

    2. Relevant equations

    Colombs Law:
    F(electric)=K((q(1)*q(2))/r^2)
    K=8.99E9

    3. The attempt at a solution

    This seems like a simple plug in problem but I'm having a little trouble.

    First i get the elementary charges of both the glass and rubber balls
    so 1.6E-19*3.5=5.6E-19 for q(1)
    and 1.6E-19*5=8E-19 for q(2)

    So i plug in the numbers i know and get:
    F(electric)=8.99E9(((5.6E-19)*(8E-19))/(.005^2))=-1.611E-22

    I plug this into the program my school uses for physics homework and it tells me im wrong.

    Can you see where im doing something wrong? please any help is appreciated.
     
  2. jcsd
  3. May 22, 2008 #2

    hage567

    User Avatar
    Homework Helper

    I don't understand why you did this. All you need to do is convert the 3.5 from microcoulombs to coulombs. Coulombs is the unit for charge.

    5 cm is not equal to 0.005 m. Check your conversion again.
     
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