CollegeBoard SAT Physics Study Guide PT1 Q44

CollegeBoard's Book

44) The problem asks us to consider the end result of the situation. In this situation, the first thing that happens is an uncharged ball comes into contact with the ball on the left. When they touch, there will be a transfer of charge by contact and the charge will average among the two balls. This means that the charge of the left ball will be cut in half. Since there is half the charge, the electrostatic force will be less than the initial force.

Where F(E) is the electrostatic force, k(c) is Coulomb's constant, Q(L) is the left ball's charge, Q(R) is the right ball's charge, and r is the distance between the two balls

We can see that the force is half the magnitude as before. It is important to know that with charges, two charges exert the same magnitude force on each other. So since the right ball and the left ball are identical and have the same mass, they will both also have the same acceleration. They will be pushed to the same angle away from each other. Since the magnitude of the force is less, they will be pushed to a shorter displacement away from each other.

Where blue is the initial situation and red is the final equilibrium situation

Answer: D