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A2L Item 147

Meta-Information
Description: 
Identify the points of a potential energy function for which the force is zero.
Goal: 
Relate force to potential energy function
Level: 
Undergraduate
Keywords: 
Forces
Keywords: 
Mechanics
Keywords: 
Potentials
Source: 
UMPERG-ctqpe66

The potential energy function for a certain body is shown at right. For which points is Fx = 0?

  1. Point 1 only
  2. Points 2 and 4
  3. Points 1 and 5
  4. Points 3 and 5
  5. Point 3 only
  6. Fx 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.