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Homework Help: Electric Forces

  1. Mar 3, 2010 #1
    1. The problem statement, all variables and given/known data
    Three charges, Q1, Q2, and Q3 are located in a straight line. The position of Q2 is 0.323 m to the right of Q1. Q3 is located 0.125 m to the right of Q2
    In the above problem, Q1 = 1.37 μC, Q2 = -2.53 μC, and Q3 = 3.43 μC. Calculate the total force on Q2. Give with the plus sign for a force directed to the right.


    2. Relevant equations

    F=kq1q2 / r^2

    3. The attempt at a solution
    I used the above formula to find the force for charge 1-2, and charge 2-3, and then added them together. I got the wrong answer.
    My answers were: 0.29867 N + 4.99 N = 5.29 N
    What am i doing wrong !?
     
  2. jcsd
  3. Mar 3, 2010 #2

    berkeman

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    Staff: Mentor

    Q1 and Q3 are both positive, but on opposite sides. Would their forces add?
     
  4. Mar 3, 2010 #3
    I added them
     
  5. Mar 4, 2010 #4

    berkeman

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    Staff: Mentor

    And got the wrong answer...
     
  6. Mar 4, 2010 #5
    Yeah I got the wrong answer.. What did I do wrong? What should I do ?
     
  7. Mar 4, 2010 #6

    berkeman

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    Staff: Mentor

    The force equation that you wrote in your original post (OP) is actually a vector equation. The forces have both magnitude and direction. You need to take that into account when you sum the forces to get the resultant.
     
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