How Do You Calculate the Charge on Spheres with Unequal Charges?

[LampMan]

Homework Statement

two charged spheres 4 cm apart attract each other with a force of 1.2x10^-9 . determin the magnitude of the charge on each if one has twice the charge (of the opposite sign) as the other.

Homework Equations

Fe = KQq/r^2

The Attempt at a Solution

well you are only given Fe and r, plus the info that Q is = to (2)q and k = 9.0x10^9 so I am stumped after this step

1.2x10^-9 = (9.0x10^9)(2)qq/16

 

[kuruman]

In your equation everything is a number except for q. Can you solve it for q? Also, you forgot to convert cm to meters.

 

[LampMan]

could it possibly be that I am using the wrong equatiom? and should be using E(force intensity) = kq/r^2 instead of coulombs law??

edit: yes i forgot to convert haha good call..but yea the fact that I am finding two charges throws me off...so would just solving for one q give me the charge I am looking for, then just double it to get the 2nd charge?

 

[kuruman]

Correct. Find q then double it. It is that simple.

 

[LampMan]

aha well I've mised 2 of 2 classes on this unit so i can't believe it was that easy now that i see it ahhh well thanks a lot