Charge and electric field?

Question

1. The problem statement, all variables and given/known data

Two particles with equal mass have charges 1.0uC and 1.0nC, respectively. What must be their mass if their mutual gravitational attraction is to overcome their Coulomb repulsion?

2. Relevant equations

F = kQ1Q2/r^2

and maybe

n = Mbody/M

3. The attempt at a solution

At first I thought I could use the first formula, where k = 9 x 10^9 Nm^2/C^2, Q1 = 1uC and Q2 = 1nC

but then i realized that

1) I don't have the distance and

2) I have no clue what the values of "u" and "n" are.

So then I thought, to use the second since I DO need the mass, but I do not know thw values of n and M.

I am lost, any help is much appreciated!!!

Thanks

Answer 1

Assuming charges are nearly point charges

with no redistribution of charge on surface areas

under consideration.

q1=1uc=1 microcoulomb = 1.0*10^-6 coulombs

q2=1nc=1 nanocoulomb = 1.0*10^-9 coulombs

k=9*10^9

G=6.67310^-11

|Force gravity|=|Force electric|

(G*m^2)/r^2=(K*q1*q2)/r^2

solving for mass

m=sqr(k*q1*q2/G)

*************************************

sqr((9*10^9)*(1.0*10^-6)*

(1.0*10^-9)

/(6.673*10^-11))  

= 367.25 kg "at least"

"to overcome"