Question

Two balls have 3 nC of excess charge and are 10cm apart. What is the magnitude of the repulsive force on each?

Electric field = 27,000
Charge = 3e-8 Coulombs

F = EQ = 8.1e-4

...which is wrong.

Answer 1

use the electrostatic force equation

also, nano is E-9

Answer 2

I still get 7.1e-4 with this equation

Answer 3

f = k Q1 Q2 /r^2 = 9E9 * (3E-9)^2 / .1^2

F = 8.1E-6 N

Answer 4

QE = 9*10^9 *3*10^-9 *3*10^-9/.1^2
= 81*10^-9/10^-2
= 81*10^-7
= 8.1*10^-6 N