# Electricity, force, and component form

1. Jan 9, 2007

### abeltyukov

1. The problem statement, all variables and given/known data

Consider the four charges in Figure P25.46 http://i137.photobucket.com/albums/q208/infinitbelt/p25-46.gif , in which d = 3 cm, q = 4 nC, the +x-axis points to the right, and the +y-axis points up. What is the force on the 1 nC charge at the bottom? Give your answer in component form, using i and j for and , respectively.

2. Relevant equations

F 2on1 = (K|q1||q2|)/r^2
F 3on1 = (K|q1||q3|)/r^2

3. The attempt at a solution

I did for force 2 on 1 :[(9 x 10^9)(5 x 10^-9)(8 x 10^-9)]/(sqrt(0.03^2 + 0.048^2))^2
Then I did tan(theta) = 4.8/3.0 = 57.994 degrees

1.12 x 10^-4 N * sin(57.994) = 9.5 x 10^-5 N

Then for the other force 3 on 1: [(9 x 10^9)(5 x 10^-9)(5 x 10^-9)]/0.03^2 = 2.5 x 10^-4 N

I am confused as to what to do from here. Any ideas?

Thanks!

2. Jan 10, 2007

### BishopUser

I'm not sure I follow your method. I know that the force on a charge due to another charge is $$F= \frac{kQq}{r^2}$$ where k is approximately $$9x10^9 N M^2 C^{-2}$$.

I'm not sure of your reasoning for plugging in 8nC or 5nC into the equation. You are also talking about q1 and q3; I don't know what those are because they aren't labeled on your diagram. Please explain your reasoning for reach step.