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Homework Help: Finding the net electrostatic force on particle 1, triangle!

  1. Sep 1, 2005 #1
    Hello everyone, Did I do the 2nd part of this problem correct? Part B. I boxed in the answer, i think it will just be easier by showing you my drawing so here is the picture -> http://img221.imageshack.us/img221/9340/phsyicss9lb.jpg [Broken]
    thanks!
     
    Last edited by a moderator: May 2, 2017
  2. jcsd
  3. Sep 1, 2005 #2

    Doc Al

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    I suggest that you recheck your arithmetic for part a. The method you used for part b looks OK (it's a bit hard to follow), but it's not the easiest way to get the answer. (You didn't take full advantage of the symmetry of the geometry.)
     
  4. Sep 1, 2005 #3
    thanks for the reply but I don't see how part A is wrong...
    F = [k(q1)(q2)]/r^2;
    F = [9.9E9*(45.0E-6)^2]/(2.70)^2 = 2.75 N
     
  5. Sep 1, 2005 #4

    Doc Al

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    The Coulomb constant (k) is about 9.0 E9, not 9.9 E9.
     
  6. Sep 1, 2005 #5
    thanks alot that woulda sucked!
     
  7. Sep 2, 2005 #6
    for the second part, i don't even think it's necessary to use trigonometry.

    consider point 3 at the origin in R2. put particles 1 and 2 at the appropriate positions in quadrant's 3 & 4. draw your force vectors for each of the forces. add them visually -- they interfere constructively directly in the +y direction. it looks to me like you'd just have to multiply your answer from a by 2, due to the geometry.

    i think it's right and a lot easier than breaking it down into components, but it looks fine barring the oofpez business.
     
    Last edited: Sep 2, 2005
  8. Sep 2, 2005 #7

    Doc Al

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    You would multiply the y-component by 2 to get the answer. But you'd still have to use some trig to find the y-component. (The answer to part a is the full force between two charges, not the y-component.)

    Note to mr_coffee: This is the approach I would use, since it takes advantage of the symmetry of the problem.
     
  9. Sep 4, 2005 #8
    So part A isn't correct? I don't see why I would need to break up part A into components if its a straight line. F = [(9E9)(45.0E-6)^2]/(2.70m)^2 = 2.5N
    The way I did my part B isn't it also correct though, even though I didn't do it the best of ways? I got a final answer of 4.33N
     
  10. Sep 4, 2005 #9

    Doc Al

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    Your solutions are perfectly OK. My only point was that there's an easier way to get part b.
     
  11. Sep 4, 2005 #10
    Oh alright, thanks for the help and i'll keep that in mind the next time! :biggrin:
     
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