# Homework Help: Electric Potential Energy Among Multiple Charges kinda a

1. Jun 3, 2010

### seto6

Electric Potential Energy Among Multiple Charges kinda aurgent

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

Four point charges, fixed in place, form a square with side length d. (See image)

http://i23.photobucket.com/albums/b354/h4llw4x0r/notSoFast.jpg

The particle with charge q is now released and given a quick push; as a result, it acquires speed v. Eventually, this particle ends up at the center of the original square and is momentarily at rest. If the mass of this particle is m, what was its initial speed v?
Express your answer in terms of q, d, m, and appropriate constants. Use k instead of 1/4πe (where e = epsilon). The numeric coefficient should be a decimal with three significant figures.

2. Relevant equations

- Electric Potential Energy equation: U = k((Q1*Q2)/r)
- Relative Kinematics Equations

3. The attempt at a solution

Ui+Ki=Uf+Kf

Kf=0
you get following
Ki=-Ui+Uf

getting the potential for each charge
solving for v
v==[((2kq^2)/dm)((9/(.5^.4))-5-((5/(2^.5))]^.5 then simplifying
i got v=[((2kq^2)/dm)(4.192)]^.5
is this correct

Last edited: Jun 3, 2010
2. Jun 3, 2010

### ehild

Re: Electric Potential Energy Among Multiple Charges kinda aurgent

ehild

3. Jun 3, 2010

### seto6

Re: Electric Potential Energy Among Multiple Charges kinda aurgent

i got it

4. Jun 3, 2010

### seto6

Re: Electric Potential Energy Among Multiple Charges kinda aurgent

v==[((2kq^2)/dm)((9/(.5^.4))-5-((5/(2^.5))]^.5 then simplifying
i should not get this v=[((2kq^2)/dm)(4.192)]^.5
i should get the following (6.24kq62/dm)^.5