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

## 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:

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

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!!

#### Attachments

• 2 KB Views: 22
• 2.1 KB Views: 21
Last edited:

haruspex
Homework Helper
Gold Member
2020 Award
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.

Edel Crine
Just redraw the graph,

Then I got,
Fx=4.032*10^(-15)N
Fy=6.12*10^(-15)N

haruspex
Homework Helper
Gold Member
2020 Award
Just redraw the graph,
View attachment 269790
Then I got,
Fx=4.032*10^(-15)N
Fy=6.12*10^(-15)N

Edel Crine
Just got new values:
Fx=1.297*10^(-15)N
Fy=1.620*10^(-15)N

haruspex
Homework Helper
Gold Member
2020 Award
Just got new values:
Fx=1.297*10^(-15)N
Fy=1.620*10^(-15)N
View attachment 269793

Edel Crine
haruspex
Homework Helper
Gold Member
2020 Award
You may have missed my edit re direction.

Edel Crine
Your are the best teacher always! I appreciate all your help in my questions! I really hope you have a nice day!

You may have missed my edit re direction.
You mean the arctan(Fy/Fx) maybe...?

haruspex
Homework Helper
Gold Member
2020 Award
You mean the arctan(Fy/Fx) maybe...?
No, I mean the signs on Fx and Fy.

Edel Crine
I think I got
Fx= +1.297*10^(-15)N
Fy= +1.620*10^(-15)N

haruspex
Homework Helper
Gold Member
2020 Award
I think I got
Fx= +1.297*10^(-15)N
Fy= +1.620*10^(-15)N
Good.

Edel Crine
Good.
Again, thank you sooooooooo much!!!