Force of repulsion of alpha particle

[adichy]

Homework Statement

An alpha particle has a mass m = 6.64x10^-27 kg and a charge q = +2e.
Compare the force of electric repulsion between two alpha
particles and the force of gravitational attraction between them. Explain briefly
why the gravitational force is ever significant, given its seeming insignificance
here.

Homework Equations

F=qE, F=kqq/r, F=ma

The Attempt at a Solution

coloumbs law can't be applied here since I am not given r
and i can't think of a way to obtain the E_field or a in f=ma when i equate qE=ma
(maybe Electric flux can be found using gauss's, but i don't think that's the right way to go)

Some guidance would be much appreciated

thanks

 

[fzero]

Both the magnitude of the electromagnetic force and that of the gravitational force depend on the distance between sources. Can you come up with a mathematical combination of the two that is independent of the distance?

 

[adichy]

im not sure how eliminate the distance

F_e=kqq/r
F_g=Gmm/r^2

equating those 2 will still leave me with distance
I can't think of any other formula for F_e that doesn't require finding the electric field or using the distance

 

[fzero]

First, go back to your text or notes and find the correct expression for the Coulomb force (what you have is the potential energy). Second, you don't really want to equate the EM and gravitational forces, but the correct expression should be clearer once you can compare the correct dependences on the separation.

 

[adichy]

oh sorry i forgot its squared...
ahh divide both the expressions to find the ratio?