# Ratio of gravitational/repulsive electrostatic force

1. Nov 28, 2009

### crybllrd

1. The problem statement, all variables and given/known data
Calculate the ratio of the magnitude of the attractive gravitational force to the repulsive electrostatic force between two protons.

2. Relevant equations
Mass of proton = M = m = 1.672e-27 kg
g = 9.80665m/s2
Q = q = 1.60219e−19 C
k = 8.9875e9 N•m2/C2

$$F_{Gravity}=g\frac{Mm}{r^{2}}$$

$$F_{electric}=k\frac{Qq}{r^{2}}$$

3. The attempt at a solution
The radius $$r$$ is not given, so I attempted to find it algebraically by plugging in numbers, and I get:

$$F_{gravity}=\frac{2.74m/s^{2}\cdot kg^{2}}{r^{2}}$$

I feel certain I am on the wrong track.

2. Nov 28, 2009

### Redbelly98

Staff Emeritus
For Fgravity you should use G, not g. I.e., not 9.8 m/s2

3. Nov 28, 2009

### crybllrd

Thanks, I changed g to G, but I'm still not sure what to do after solving for r

4. Nov 29, 2009

### Redbelly98

Staff Emeritus
Don't solve for r, just leave it in the form