# Finding the net electrostatic force on particle 1, triangle!

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!

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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.)

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

Doc Al
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The Coulomb constant (k) is about 9.0 E9, not 9.9 E9.

thanks alot that woulda sucked!

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.

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Doc Al
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teclo said:
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.
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.

(The answer to part a is the full force between two charges, not the y-component.)

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

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.

Oh alright, thanks for the help and i'll keep that in mind the next time! 