Question

A point charge +Q is fixed on a very large horizontal frictionless tabletop. A second point charge +q is released from rest near the stationary charge and is free to move. Which statement best describes the motion of +q after it is released?

A point charge +Q is fixed on a very large horizontal frictionless tabletop. A second point charge +q is released from rest near the stationary charge and is free to move. Which statement best describes the motion of +q after it is released?

	Its speed will be greatest just after it is released.
	As it moves farther and farther from +Q, its speed will decrease.
	Its acceleration is zero just after it is released.
	As it moves farther and farther from +Q, its speed will keep increasing.
	As it moves farther and farther from +Q, its acceleration will keep increasing.

Answer 1

a) false, there is an initial force, which means there is an initial acceleration

b) false, the speed is zero initially then increases.

c) false, as the distance goes up, the force goes down (it's inversely proportional to distance squared), so the acceleration goes down also.

d/e) these are complicated. The problem is that there is a repulsive force that causes an initial acceleration that causes an increasing velocity. But as the charges separate, the force decreases, so the acceleration decreases.

But bottom line, the acceleration is always positive although decreasing, so the speed is always increasing. which means (d) is false, and (e) is true