# Charges problem.

1. Jan 27, 2004

### NINHARDCOREFAN

Four charges are arranged in (x,y) plane:
-3nC at (-4, 1)
-4nC at (0, 0)
-6nC at (5, 3)
-7nC at (4, 5)

Find the magnitude of the resulting force charge at the origin(0, 0).

I know how to find radius:
R1(squared) = 17
R2(squared) = 0
R3(squared) = 34
R4(squared) = 41

But I don't know which charges to use in the equation to find four different forces:
F=(K*q1*q2)/r(sqared)
K = 8.99 * 10^9

2. Jan 27, 2004

### himanshu121

Find the field at the origin by other charges exluding the one which is placed at the origin(* NOTE *) Add vectorially

3. Jan 27, 2004

### NINHARDCOREFAN

posted the question wrong

Find the magnitude of the resulting force on the -4nC charge at the origin.

And radius' are suppose to be from that charge, so they are only 3 radius.

4. Jan 27, 2004

### himanshu121

Yes , but F is vector u can not add only magnitudes it has to be done in proper manner

5. Jan 27, 2004

### NINHARDCOREFAN

Tell me if I'm doing this right, I'm getting big numbers thta's why I have a doubt:

F1 = 8.99e9*4e-9*3e-9/17 = 6.346e-9
F2 = 8.99e9*4e-9*6e-9/34 = 6.346e-9
F3 = 8.99e9*4e-9*5e-9/41 = 4.385e-9

Ang1= tan^-1(1/-4) = -14.04
Ang2= tan^-1(3/5) = 30.96
Ang3= tan^-1(5/4) = 51.3

Am I right so far?

6. Jan 27, 2004

### himanshu121

Let the forces be in form Kq1q2/r^2

Yes angles are correct but what are the directions of these vectors??

After finding the direction resolve the components along x&y axis And now add the components