posted by Lindsey .
Point charges Q1 = 50 µC and Q2 = -20 µC are placed 2 meters apart. Where can I put a third charge so that the net electrical force on it is zero?
I'm a little rusty on this, but I think you need the charge of the one that you are putting in the middle. Was that provided to you?
I apologize, you do not have to know it, it is not needed.
Let the distance between Q1 and Qo equal x(r1), and the distance between Q2 and Qo equal x-2m (r2).
Using the sum of forces,
Ko and Qo cancel each other out leaving
Plugging in my values for Q1 and r, and r2
(50 x10^-6 C/x^2)=( -20 x10^-6 C)/(2-x)^2
Since they are both in µ C, rewrite the equation as
factoring out 10,
Use the quadratic equation to solve for x
I hope this helps, but I am not that positive.
Last set of values should read: