# Electric Potential of 2 Point Charges

1. Jun 9, 2012

### vforvirginia

1. The problem statement, all variables and given/known data
The 2.1mm diameter spheres in the figure are released from rest. What are their speeds vc and vd at the instant they collide?

Spheres:
C has 2nC of charge and a mass of 1g.
D has -1nC of charge and a mass of 2g.
The starting distance between the two spheres is 10mm. Each sphere as a diameter of 2.1mm.

2. Relevant equations
V=(1/4pi*ε_0)*Q/r
Q is the charge and r is the distance between the two spheres.
K=.5*mv^2

3. The attempt at a solution
ΔKC+ΔUC = 0 = ΔKD+ΔUD
Ki for spheres C and D are 0 since the spheres begin at rest:
KCf+UCf-UCi=KDf+UDf-UDi

The rest of my attempt is basically putting the numbers in and solving for KCf in terms of KDf and then using that to get KDf. I just want to know if I am heading in the right direction.

2. Jun 9, 2012

### Infinitum

Hi vforvirginia! welcome to pf!!

In your energy conservation equations you are comparing the energies of two different balls and making them equal. I think that should be re-framed as, the total energy of the balls initially is equal to their total energy at the end.