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Help with Coulombs Law

  1. Jan 23, 2012 #1
    1. The problem statement, all variables and given/known data
    Consider three charges q1 = 4.3 nC, q2 = 6.6 nC, and q3 = -2.3 nC, arranged in a triangle as shown below.

    (a) What is the electric force acting on the charge at the origin?
    N, ° counterclockwise from the negative x-axis

    (b) What is the net electric field at the position of the charge at the origin?
    N/C, ° counterclockwise from the negative x-axi
    picture of problem
    http://www.webassign.net/holtphys/p16-38alt.gif

    2. Relevant equations
    F=kQ1Q2/r^2


    3. The attempt at a solution


    which way is counterclockwise
     
  2. jcsd
  3. Jan 23, 2012 #2
    If it's counterclockwise from the negative x-axis, start from the left x-axis then go down.
     
  4. Jan 23, 2012 #3

    SammyS

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    Find a watch with a second hand. Set it at the origin, face up. The second hand has a clockwise rotation. the opposite rotation is counter-clockwise.
     
  5. Jan 23, 2012 #4
    What is the net electric field at the position of the charge at the origin? How do you find this
     
  6. Jan 23, 2012 #5
    You're essentially finding the force exerted by a charge on an infinitesimally small positive charge, which happens to be placed at the origin.

    electric field = kQ/r^2
     
  7. Jan 23, 2012 #6
    does the nC stand for 10^-9
     
  8. Jan 23, 2012 #7
    Yes, the n stands for nano, [itex]10^{-9}[/itex]
     
  9. Jan 23, 2012 #8
    how do you find part a.
     
  10. Jan 23, 2012 #9
    Have you attempted to solve it?
     
  11. Jan 23, 2012 #10
    I have my last answers were
    (a) What is the electric force acting on the charge at the origin?
    2.838e-6 N, -8.901e-6 ° counterclockwise from the negative x-axis

    (b) What is the net electric field at the position of the charge at the origin?
    4.3e11 N/C, 3.87e12 ° counterclockwise from the negative x-axis BUT THEY WERE WRONG
     
  12. Jan 23, 2012 #11
    Could you post your work?
     
  13. Jan 23, 2012 #12
    (9*10^9)*(-2.3*10^(-9))*(4.3*10^(-9))/0.10^2

    (9*10^9)*(4.3*10^(-9))*(6.6*10^(-9))/0.30^2 counterclockwise

    net electric field
    (9*10^9)*(4.3*10^(-9))/0.30^2
    (9*10^9)*(4.3*10^(-9))/0.10^2
     
  14. Jan 23, 2012 #13
    someone please help this is due tomorrow and I cannot figure it out!!
     
  15. Jan 23, 2012 #14
    For part a, you used Coulomb's law to find the force exerted by each charge on the charge at the origin. Have you paid attention to their directions? If you draw them as vectors, how would the resultant vector look?

    And for electric field, you want to use the other charge as the Q you're using.
     
  16. Jan 23, 2012 #15
    do i need to then find the hypotunse
     
  17. Jan 23, 2012 #16
    i dont understand why I need a counterclockwise one arent they the same
     
  18. Jan 23, 2012 #17
    You want to find the magnitude, and the direction (angle)
     
  19. Jan 23, 2012 #18
    Nothing has helped
     
  20. Jan 23, 2012 #19
    how do i find the direction angle I was given no number for an angle
     
  21. Jan 23, 2012 #20
    You should have the two perpendicular force vectors starting at the origin; they form a right triangle... If you have the two legs of a right triangle, you should be fine figuring out the rest of the parts of the triangle.
     
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