# Struggling with Electric force... The Superposition Principle

When I'm solving a superposition principle problem i get stuck and so confused with the signs.
For example this problem

Consider three point charges at the corners of a triangle, as shown at right, where q1 = 6.00 × 10−9 C, q2 = −2.00 × 10−9 C, and q3 = 5.00 × 10−9 C. Find the magnitude and direction of the resultant force on q3.

I know that first i find the magnitude of each force... F3,1 and F3,2. I'm ok with this part
But then when finding the x and y components of each individual force I get so confused as to what sign I should use!!

jtbell
Mentor
when finding the x and y components of each individual force I get so confused as to what sign I should use!!

The x component is usually horizontal, in which case left is negative and right is positive. The y component is usually vertical, in which case up is positive and down is negative. Draw a diagram that shows the vectors and their components. You should be able to see the directions and assign the +/- signs accordingly.

The x component is usually horizontal, in which case left is negative and right is positive. The y component is usually vertical, in which case up is positive and down is negative. Draw a diagram that shows the vectors and their components. You should be able to see the directions and assign the +/- signs accordingly.

Thank you!! This helped so much