# Can you check this? - Charges and Forces

• Albeaver

#### Albeaver

Can you check this? -- Charges and Forces...

## Homework Statement

A +3-mC charge and a -4-mC charge are fixed in position and separated by 5 meters.
A)Where could a +7-mC charge be placed so that the net force on it is zero?
B)Where could a -7-mC charge be placed so that the net force on it is zero?

I came up with this diagram:
|---------------5m------------------|
*----------------*------------------*
q q q
|-------r------|----------r----|

## Homework Equations

F=K(|q*q|)/r^2
F=K(|q*q|)/r^2
r+r=5
k=8.99*10^9
|q|=4
|q|=3
|q|=7

## The Attempt at a Solution

F=F<---Because they are equal
K(q*q)/r^2=K(q*q)/(5-r)^2<---We get (5-r)=r from r+r=5 solved for r)
Then after we solve for r we get this:
r=5*√(q)*(√(q)-√(q))/(q-q)

So that means that both the +7-mC charge and the -7-mC charge are in the same position. The number I got was r=2.32m and r=2.68m. Did I set this up, and execute this correctly?
Thank you very much for your time.