# Homework Help: Electric charges and forces

1. Jan 11, 2008

### sam.

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

A 10.0 nC charge is located at position (x, y) = (1.0 cm, 2.0 cm). At what (x, y) position(s) is the electric field
a. -225,000i N/C
b. (161,000i + 80,500j) N/C
c. (28,800i + 21,600j) N/C

2. Relevant equations

E = (1/4$$\pi$$$$\epsilon$$)(q/r^2)
F = Kq_1q_2/r^2

3. The attempt at a solution

With a) I used the Pythagorean theorem to find r^2 using (x, y) which is squareroot 5. However, I'm not exactly sure where this gets me. I honestly have no clue as to where to start with this question and any help would be greatly appreciated!

2. Jan 11, 2008

### dynamicsolo

I think you probably ought to show that calculation. I get for part (a) that the distance from the charge is 2 cm.

In each part, use the field magnitude to find the radius of the circle centered on the 10 nC charge on which the point could be found. You will want to make a picture of the way the field points. Since the charge is positive, the field points outward from it; where would the "test point" need to be on each circle in order to have those field vector components? (The direction can be found by the appropriate use of trigonometry.)