Physics 101- Introduction to Mechanics
April 29- SHO & Pendulums






  Reading Energy Graphs

Two atoms interacting with each other have the potential energy shown in the figure.  You may assume that the massive atomís mass is much larger than the light atomís mass, the light atom can only move along the x axis, and U(x) -> 0 smoothly as x -> infinity.

Imagine that at t=0, the little atom is at rest at x=0.2nm.  What is the closest that it will ever get to the big atom subsequently (in the absence of external effects)?
  1. 0.03nm
  2. 0.05nm
  3. 0.2nm
  4. other

If the system has total energy of +3 x 10-21J and the little atom is at x=0.11nm at t=0 the atoms are

  1. Bound
  2. Unbound
  3. It depends on the little atomís initial direction of motion
  4. Depends on the atomís initial speed
Imagine that the little atom approaches the big atom from infinity with an initial K= 5 x 10-21J.  How close to the big atom does it get?
  1. x=0
  2. x=0.04nm
  3. x=0.11nm
  4. x=0.2nm
  5. x=0.3nm
  6. other

Imagine that at t=0, the little atom is at position x=0.11nm and has a kinetic energy of 5 x 10-21J.  About how much energy would we have to add to break the bond?

  1. 1x10-21J
  2. 6x10-21J
  3. 12x10-21J
  4. none: the bond is already broken


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Jeff Phillips
Loyola Marymount University
Spring 2002