Point charges arranged as a trianngle

[jenzao]

Homework Statement

Consider three charges at the vertices of an equilateral triangle of side a = 7 cm. qA = +2 µC, qB = +2 µC, and qC = -1 µC. (see attached picture)

Find the x- and y- components of the electric force acting on qC

Homework Equations

i am doing everything right, but getting wrong answer ?

The Attempt at a Solution

x-comp cancel obviously, so I am left with finding y-comp...

F = kqAqC/r^2
= 2.571e-1

sin60(2.571e-1) = 2.2266e-1
multiply by 2 = 4.453e-1 N (this is wrong though)

i can't see the prob. The forces both point in positive y direction, so the y vectors sum
please help, thanks!

 

[rootX]

The Attempt at a Solution

x-comp cancel obviously, so I am left with finding y-comp...

F = kqAqC/r^2
= 2.571e-1

sin60(2.571e-1) = 2.2266e-1
multiply by 2 = 4.453e-1 N (this is wrong though)

=k.qA.qC/r^2
=9E9 x 2E-6 x 1E-6/0.07^2
=3.67

I see you are dividing by 7
Two mistakes it's 7cm and then its r^2