I am having trouble understanding this problem in Electric Potential. (Source: OpenStax, Chapter 19) Now consider another system of two point charges. One has a mass of 1000 kg and a charge of 50.0 µC, and is initially stationary. The other has a mass of 1.00 kg, a charge of 10.0 µC, and is initially traveling directly at the first point charge at 10.0 m/s from very far away. What will be the closest approach of these two objects to each other? Here is my attempt: Spoiler The internal energy of the system is conserved. Therefore, we have: KE1+PE1=KE2+PE2 The potential energy at time 1 is essentially 0, and the kinetic energy at time 2 is 0. PE=qV. Therefore, the equation becomes: 0.5(1)(10)2 + 0 = 0 + (10*10-6)V 50=(10-5)V 5,000,000=V This number is implausible. I also used V=kq1q2/R 5,000,000=kq1q2/R 5,000,000=(9*10-9)(10*10-6)(50*10-6) / R Solving for R, I got R=9*10-9m However, the correct answer was R=9*10-2 m, or 9 cm. What did I do wrong?