# Homework Help: Ratio of Electric Force to Gravitational force

1. Aug 23, 2007

### Winzer

1. The problem statement, all variables and given/known data
It is known that the electric force of repulsion between two protons is much stronger than their gravitational attraction. For two protons a distance R apart, calculate the ratio of the magnitude of the repulsion to that of the attraction.

2. Relevant equations
$$F_{g}=\frac{Gm_{1}m_{2}}{r^2}$$
$$F_{e}=\frac{Kq_{1}q_{2}}{r^2}$$

3. The attempt at a solution
So the ratio $$\frac{F_{e}}{F_{g}}$$ =$$\frac{Kq^2}{Gm^2}$$
I get 1.3E28 which is wrong. Why?

2. Aug 23, 2007

### Dick

The equation is right. Hard to tell where you are going wrong with putting the numbers in.

3. Aug 23, 2007

### Winzer

K=9.0E9
G=6.67E-11
Mass of proton aprox. 1.672E-27
Charge of a proton 1.602E-19
Right?

4. Aug 23, 2007

### Dick

Fine. But looking at your number, I think you are forgetting to square the masses and charges.

5. Aug 23, 2007

### Winzer

ok, i get 1.2E36 with 2 sig figs and still wrong.

6. Aug 23, 2007

### Dick

I get 1.2355E36. So I disagree with who or whatever is telling you it's wrong.