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Homework Help: Expressing force as a vector

  1. Feb 3, 2009 #1
    1. The problem statement, all variables and given/known data
    I have a charge Q of +1.5*10^-7C located at co-ordinates (x,Y) (-6cm,0cm)
    what is the force due to Q on a test charge of +1 C at the origin. Expressed as a vector.

    3. The attempt at a solution
    F= [tex]\frac{\kappa*Q1*Q2}{r^2}[/tex]

    F= [tex]\frac{8.99*10^{9}*1.5*10^{-7}*1}{.06^{2}}[/tex]

    F= 3.746*10 [tex]^{5}[/tex] N repulsive force.

    How do I express this in [tex]\widehat{i}[/tex], [tex]\widehat{j}[/tex] unit vector notation?
  2. jcsd
  3. Feb 3, 2009 #2


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    Homework Helper

    Your vector coordinates are (-6,0) making the repulsive force -x.

    I'd say then it's:
    F = - (your answer) i + 0 j
  4. Feb 3, 2009 #3
    Okay, thanks. What if the test charge wasn't located at the origin but at (0,7) so that it made a right triangle with Q.
    Could I "move" the test charge to the origin and calculate the x coordinate and then "move" Q to the origin and calculate the y coordinate?
    Or is this wrong?
  5. Feb 3, 2009 #4


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    Homework Helper

    The Force at the origin (0,0) is what you wanted isn't it.

    It's repulsive from the (-6,0) charge, so then at the origin it will be +x directed, not -x directed as it is on the charge at (-6,0).

    So in that case the repulsive force is F = +(your answer) i + 0 j
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