Two identical +9.0 µC point charges are initially spaced 5.2 cm from each other. If they are released at the same instant from rest, how fast will they be moving when they are very far away from each other? Assume they have identical masses of 1.0 mg.

Answer 1

Potential energy of the charges is
PE=k•q^2/r=9 •10^9•(9•10^-6)^2/0.052=14 Joules.
According to the Law of conservation of energy
PE=2KE
KE=mv^2/2.
2KE= mv^2 =PE
v=sqroot(PE/m)=sqroot(14/10^-3)=118.3 m/s.