Two particles each have a mass of 7.7 x 10-5 kg. One has a charge of +5.9 x 10-6 C, and the other has a charge of -5.9 x 10-6 C. They are initially held at rest at a distance of 0.91 m apart. Both are then released and accelerate toward each other. How fast is each particle moving when the separation between them is one-half its initial value? mass particle = 7.7x10^-5 kg q1 = 5.9x10^-6 C q2 = -5.9x10^-6 C r0 = .91m r1 = .455m v0 = 0 m/s v1 = ??? 2. Relevant equations F = kq1*q2/(r^2) KE = .5 * m * v^2 3. The attempt at a solution I believe the first thing to do would be to gather the force between the charges, using F = k*q1*q2/(.91^2). The next thing I think I should do is substitute F in for KE, in the equation KE = .5 * m * v^2 One of the problems I'm not sure about is how the KE equation factor in two charges moving in opposite directions. By substituting F for KE, am I already factoring in all the vectors I need? edit: I think another way of describing what I'm feeling is: Is the velocity in the KE equation the velocity of each charge, regardless of direction?