# Homework Help: Finding the x-component of a force using Coulomb's Law

1. Apr 6, 2012

### cherrymilk

1. The problem statement, all variables and given/known data
(1) A point charge q1 = -2.9 μC is located at the origin of a co-ordinate system. Another point charge q2 = 5 μC is located along the x-axis at a distance x2 = 8.6 cm from q1.

The answer to this was -17.64N.

(2) Charge q2 is now displaced a distance y2 = 2.4 cm in the positive y-direction. What is the new value for the x-component of the force that q1 exerts on q2?

2. Relevant equations
Coulomb's Law: F = k (q1q2)/(r^2)

3. The attempt at a solution
Seeing that q2's position had changed, I calculated the new force exerted using Coulomb's Law. I used 9*10^9 for k, and using the Pythagorean theorem, I calculated the new distance between the charges, which I got to be 0.089. After using Coulomb's Law, I got an answer of -16.37N. To find the x-component, I multiplied this value by cos(45), giving me a final answer of -11.58. This, however, is apparently incorrect and I'm confused as to why.

Any help would be appreciated!

2. Apr 6, 2012

### OtherWindow

Why did you chose 45 degrees as the angle?

3. Apr 7, 2012

### cherrymilk

Ah, I see what I did wrong. I just assumed that because they had drawn the line they way they did in the figure, the angle was 45 degrees. Silly mistake, thanks for that!

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