# Homework Help: Need help using Coulomb's Law to find unkown charge

1. Jan 23, 2005

### azsktbrdr

Hi, the problem states the following. "Charge q2 is in static equilibrium. What is q1?"

I've attached the image of the problem I'm working on. From the looks of this it should be quick and simple it seems, but I am having a tough time with it. I would appreciate any help you can offer.

With q2 being in static eq., I thought that meant that all forces on q2 sum to zero, so I tried to add the forces from q1 and the center charge up and set equal to zero and solve for q1, but I'm not sure if this is right. Also, I put in the assumption that q1 and q2 are equal and I don't know if that is true, either.

#### Attached Files:

• ###### Charges.jpg
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2. Jan 23, 2005

### kenhcm

You do not need to assume that q1 and q2 are equal. Basically, you just need to write down the force exerted on q2 by q1 and the center charge respectively. Equate these two expressions and solve for q1.

Best regards,
Kenneth

Last edited: Jan 23, 2005
3. Jan 23, 2005

### azsktbrdr

Kenneth,

Thanks for the help. I can't believe I didn't notice that the q2's would cancel when you equate the two. Yikes, I need to get to bed before I do any more damage :zzz: