Net electric force of multiple charged particles in 3-d space

  • Thread starter Edel Crine
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Homework Statement:

An xyz coordinate system contains three charged particles: particle 1, q1=-5.0 muC, at (4.0m,-2.0m,0); particle 2, q2=12 muC, at (1.0m, 2.0m, 0); and an electron at (-1.0m,0,0).
(a) Draw a diagram showing the vectors you need in order to determine the direction of the separate electric forces exerted on the electron by particles 1 and 2.
(b) Calculate the vector sum of these two forces.

Relevant Equations:

f=k((q1*q2)/r^2)*unit vector r
I draw the graph like this:
234.png

For (b), I divided each force vector to e from p1 and p2 as x and y parts.
1.png

I computed them and got
Fx=-4.608*10^(-15)N
Fy=-2.52*10^(-15)N

However, I am not sure whether I did it correctly or not...
I appreciate every help from all of you!!
Thank you!!
 

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  • #2
haruspex
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You missed out a chunk of your working, and I don't have time to check your final result right now, but I notice the directions of the arrows in your diagram. Are these intended to represent the directions in which the forces will act? Note that the two particles are oppositely charged.
 
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  • #3
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Just redraw the graph,
234.png

Then I got,
Fx=4.032*10^(-15)N
Fy=6.12*10^(-15)N
 
  • #5
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I get somewhat smaller numbers. Please post your detailed working.
Just got new values:
Fx=1.297*10^(-15)N
Fy=1.620*10^(-15)N
2.png
 
  • #7
haruspex
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Those numbers look about the right magnitude. What about direction?
You may have missed my edit re direction.
 
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  • #8
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Those numbers look about right.
Your are the best teacher always! I appreciate all your help in my questions! I really hope you have a nice day!
 
  • #9
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You may have missed my edit re direction.
You mean the arctan(Fy/Fx) maybe...?
 
  • #10
haruspex
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You mean the arctan(Fy/Fx) maybe...?
No, I mean the signs on Fx and Fy.
 
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I think I got
Fx= +1.297*10^(-15)N
Fy= +1.620*10^(-15)N
 
  • #12
haruspex
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I think I got
Fx= +1.297*10^(-15)N
Fy= +1.620*10^(-15)N
Good.
 
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