**Goal:** Relate force to potential energy function

**Source:** UMPERG-ctqpe66

The

potential energy function for a certain body is shown at right. For

which points is F_{x} = 0?

- Point 1 only
- Points 2 and 4
- Points 1 and 5
- Points 3 and 5
- Point 3 only
- F
_{x}not equal to 0 anywheree

## Commentary:

## Answer

(4) The force is given by the negative of the slope of the

potential function. Points 3 and 5 are equilibrium points, but only 3 is

a stable equilibrium point. Students frequently choose answer #2

thinking that the force is zero at these points.