Need help with Electric Potential problem.

[PhysicsGnome]

I was going over that mit open courseware stuff and I ran into a problem I'm having trouble with...

http://www.phy.mtu.edu/~gagin/2200/textfiles/ph2200-ex2-f05.pdf

#23

The equation I have for it is:

vi = sqrt(2/m * ((K*1.5nC*e/.005m) + (K*1.5nC*e/.005m)))

But I'm getting to large a value... I've been playing around with it but can't seem to get it.

Thanks for any help.

 

[qspeechc]

First consider the proton between the charge and its total energy (it will be all potential). Then consider the particle very far away, such that it has zero potential energy, and all kinetic energy.
The formula for electrical potential energy is

-k(Q1)(Q2)/r

between any two point charges of charge Q1 and Q2, r the distance between them. We can evaluate the potential between the proton and one charge and multiply by two because the situation is symmetrical.