# Homework Help: A electrostatics problem

1. Aug 18, 2009

### Rajat jaiswal

Friends,
I am not being able to solve the following problem i would be grateful if any one could help me out.
here is the problem:
eight equal point charges each of charge q and mass m are placed at eight corners of a cube of side a.
if keeping all other charges fixed a charge at a single corner is released then find out the speed when it is at infinite distance.
even advices on how to proceed would help.
Thank you.

2. Aug 18, 2009

### kuruman

Your initial configuration is 8 charges assembled at the corners of a cube. Your final configuration is seven charges at the corners of a cube and one charge at infinity with some kinetic energy. Energy conservation says

Kinitial+Uinitial = Kfinal+Ufinal

Replace each of the four symbols above with appropriate expressions.

3. Aug 18, 2009

### Rajat jaiswal

Thanks a lot,
could you please explain me how to find out the energy of the charge at infinity.
Also can anyone explain me the effect of electric field on a dielectric(non- conducting) medium .

4. Aug 18, 2009

### tms

It's usually easiest to define the potential energy at infinity to be zero.