# Electrical Potential Energy

1. Sep 5, 2005

### ussrasu

I have no idea what principles i am supposed to use in this question? Could someone show me how to do this question please? Thanks

Calculate the electrical potential energy of two protons separated by 1 nm, and compare it with their gravitational potential energy. Estimate how heavy hypothetical particles (with the same charge e) must be in order not to repel each other.

2. Sep 5, 2005

### whozum

Find the EPE and find the GPE, compare how strong they are. Then find the mass that each proton would need to have so that their gravitational attraction would equal their electromagnetic repulsion.

3. Sep 7, 2005

### ussrasu

I dont know how to do it - with the small amount of info given? Can someone show me how to work it out please?

Thanks!

4. Sep 7, 2005

### whozum

You should try doing your own homework.. that problem is very do-able, all the information is given.

5. Sep 7, 2005

### HallsofIvy

Staff Emeritus
"potential energy" is equal to the work done in separating the objects.

Imagine one of the protons and calculate the work done in moving the other from a distance of infinity to 1m (I started to say from 0 to infinity but that's the wrong way- the force between them is infinite at 0 distance!).

The work is, of course, $$\int_{x= \infty}^1 F(x)dx$$ where F(x) is the force at distance x.

For gravity that is $$F(x)= \frac{-Gm^2}{x^2}$$ and for electrical force that is $$F(x)= \frac{q^2}{x^2}$$ where m and q are the mass and charge on the proton. (Am I missing a constant in the electrical force formula- this isn't my "area of expertise!)

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