# Homework Help: Electrostatic and gravitational potential energy question

1. Jun 30, 2004

### Sigma Rho

Hi all,

I have a few questions that I'd appreciate some guidance on.

There are two identical dust particles:-
mass 13ug
charge +9.8E-15 C
electrostatic potential energy 8.7E-17 J
gravitational potential energy 1.1E-24 J

The mass is given in the question, the energies I calculated. The part of the question that I am having problems with asks me to comment on these values of energy, with reference to the zero points of each.

Apart from saying that there's a lot more electrostatic potential energy than there is gravitational, and that electrostatic force is much more powerful than gravitational force, I don't really know what else to say. Do I need say more than that?

It then asks for the total potential energy of the system, which I haven't seen mentioned in the text book (or maybe I just didn't read it properly ). Is this just the algebraic sum of the electrostatic and gravitational energies, or is there something else to consider?

How does this change as the seperation of the particles changes? I guess I can work this out once I've mastered the question above.

I'm not looking for actual answers to these, I'd rather work them out for myself, but any guidance would be greatly appreciated.