Force between two charged particles at a distance question, help please?

[kirsten_2009]

Homework Statement

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?

Homework Equations

F = q1 x q2 / d^2

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!

 

[Doc Al]

F = q1 x q2 / d^2

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

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)

Good!

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?

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.

 

[kirsten_2009]

Hello Doc Al,

Thanks for your reply and help...so...would this be correct?

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!

 

[Doc Al]

Hello Doc Al,

Thanks for your reply and help...so...would this be correct?

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

Looks good!