# Homework Help: Find the Resultant Force

1. Sep 11, 2009

### tag16

1. The problem statement, all variables and given/known data
Particle A with a charge of 45 micro Coulombs is located on the x-axis at a point -11 cm from the origin. Particle B with a charge of 41 micro Coulombs is located on the y-axis at a point +68 cm from the origin. What is the magnitude of the electrostatic force that Particle A exerts on Particle B? (Answer in Newtons.)

2. Relevant equations

Coulomb's Law: Fe=ke(q1q2/r^2)

3. The attempt at a solution

(8.99x10^9)((45x10^6)(41x10^6))/11^2

(8.99x10^9)((41x10^6)(41x10^6))/2(68^2)

Not sure what to do next or if this is even right so far. I think I have to do something w/ the x and y components and find the degree of the angle, which I'm not sure how to do.

2. Sep 11, 2009

### rl.bhat

First of all convert distances from cm to meter. Then find the distance r between A and B.
Now using the relevant equation find the force on B by A.

3. Sep 12, 2009

### tag16

so would it be (8.99x10^9)((4.5x10^-5)(4.1x10^-5))/(.79)^2 ?

4. Sep 12, 2009

### tag16

what do you have to do differently when one charge is on the x axis and the other is on the y axis as appose to them both being on the x axis and you just add them together?

5. Sep 12, 2009

### rl.bhat

The distance between A and B is sqrt(OA^2 + OB^2)
O.79 m is the distance between A and B if they are on the x axis.

6. Sep 12, 2009

### tag16

so what if one of the charges is on the y axis?

7. Sep 12, 2009

### rl.bhat

Then the distance between A and B is sqrt(OA^2 + OB^2)