# Homework Help: Force between two charged particles at a distance question, help please?

1. Oct 14, 2014

### kirsten_2009

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

Two small electrically charged objects are placed 6 centimeters (cm) apart, where they exert a force of 8 N on each other. How far apart must they be placed in order to exert a force of 1 N on each other? Assuming that the charges on the two objects are equal, what is the charge?

2. Relevant equations

F = q1 x q2 / d^2

3. The attempt at a solution

This questions seems to be simple to me, yet, I don't know why I'm so stuck...so....here is my reasoning:

If at 6 cm, the force = 8N and we want to find out what the distance between the charged particles is when the force between them is 1N...I'm assuming that they would have to be further apart so the force between them decreases by a magnitude of 8 times....and since the force weakens as the distance between the particles is squared then: square root of 8 = 2.82 x 6 cm = 16.97 cm? (I'm not sure if that is correct) and then to find the charge on the particles...I'm at a loss...but assume that if the above calculation is correct; I could substitute the values into the equation and clear for q^2? Thanks in advance for any help you can give me!

2. Oct 14, 2014

### Staff: Mentor

Don't forget the constant k (Coulomb's constant).

Good!

This problem has nothing really to do with the first part. Just pick one of the distances, plug the given data into Coulomb's law, and solve for the charge. Careful with units! And don't forget that constant.

3. Oct 14, 2014

### kirsten_2009

Hello Doc Al,

F=9x10^9 * q1 x q2 / d^2
1N=9x10^9 * q^2 / 0.1697m^2
q=√0.0288m x 1N / 9x10^9
q=1.78 x 10^-6 Coulombs

Thanks so much!

4. Oct 14, 2014

Looks good!