# Electric Potential two metal balls find final velocities

1. Feb 7, 2012

### Cisneros778

1. The problem statement, all variables and given/known data
Two metal balls of mass m1 = 2 g (diameter = 2 mm) and m2 = 6 g (diameter = 6 mm) have positive charges of q1 = 2 nC and q2 = 7 nC, respectively.

A force holds them in place so that their centers are separated by 8 mm. What will their velocities be after the force is removed and they are separated by a large distance? (Enter the magnitudes of the velocities.)
v1 =
v2 =

2. The attempt at a solution
intiial potential energy of the system E= kq1q2/d
d = .008 m
k = 9 x 10^9
.5m1v1^2 + .5m2v2^2 = E
as there are no external force on the total system momentum is conserved???
m1v1 = m2v2

2. Feb 8, 2012

### Fightfish

Yes. The momentum of the system is conserved.
Conservation of energy + conservation of momentum will solve the problem.
The key is to recognize what happens when the two charges are separated by a large distance ie. distance d between them tends towards infinity.