One particle has a mass of 3.00 10-3 kg and a charge of +8.00 C. A

Question:

One particle has a mass of 3.00 × 10-3 kg and a charge of +8.00 µC. A second particle has a mass of 6.00 × 1023 kg and the same charge. The two particles are initially held in place and then released. The particles fly apart, and when the separation between them is 0.100 m, the speed of the 3.00 × 10-3 kg particle is 125 m/s. Find the initial separation between the particles.