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B Struggling with Electric force... The Superposition Principle

  1. May 13, 2016 #1
    When I'm solving a superposition principle problem i get stuck and so confused with the signs.
    For example this problem

    Consider three point charges at the corners of a triangle, as shown at right, where q1 = 6.00 × 10−9 C, q2 = −2.00 × 10−9 C, and q3 = 5.00 × 10−9 C. Find the magnitude and direction of the resultant force on q3.

    I know that first i find the magnitude of each force... F3,1 and F3,2. I'm ok with this part
    But then when finding the x and y components of each individual force I get so confused as to what sign I should use!!
  2. jcsd
  3. May 13, 2016 #2


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    Staff: Mentor

    The x component is usually horizontal, in which case left is negative and right is positive. The y component is usually vertical, in which case up is positive and down is negative. Draw a diagram that shows the vectors and their components. You should be able to see the directions and assign the +/- signs accordingly.
  4. May 13, 2016 #3
    Thank you!! This helped so much
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