Question

Two charges of +8.0mC and -6.0 mC attract each other with a force of 3.0x103 N in a vacuum. What is the distance between the charges.

Answer 1

Given:

$q_1=\rm 8.0\:mC=8.0*10^{-3}\:\rm C$

$q_2=\rm 6.0\:mC=6.0*10^{-3}\:\rm C$

$F=\rm 3.0*10^{3}\:\rm N$

The Coulomd law says

$$F=k\frac{q_1q_2}{r^2}$$

Hence, the distance between the charges

$$r=\sqrt{\frac{kq_1q_2}{F}}\\ =\sqrt{\frac{9*10^9*8.0*10^{-3}*6.0*10^{-3}}{3.0*10^{3}}}=12\;\rm m$$