Two identical balls of mass m and charge q are released from rest when they are a distance d apart. Assuming the only force each ball experiences is due to the repulsion between the like charges, which of the following expressions can correctly be solved to find the speed of each ball when the balls are 3d apart?

1. ½ mv2

   =

   kq2 2d

2. ½ mv2

   =

   kq2 d

3. ½ mv2

   =

   kq2 d

   –

   kq2 3d

4. mv2

   =

   kq2 2d

5. mv2

   =

   kq2 d

   –

   kq2 3d