Problem Solving Guidelines

The following general guidelines are intended to help you learn how to approach the more advanced problems you will encounter in this class.  These techniques should apply equally well in other Physics courses.  I have developed these techniques through my experience.  There is no single way to solve problems; if you have already developed some methods that work for you, then by all means, stick with them.  But for those who feel they are struggling a bit, I hope these guidelines will help you get moving in the right direction.  I'm sure that once you gain some experience with solving problems, you will also develop your own personal style.
 
  1. Carefully read the statement of the problem.
  2. Make a diagram(s) for the problem.  Include any objects, forces, and motions mentioned in the statement of the problem.  Artistic quality is not an issue, as long as you can visualize what is occuring through the drawing.
  3. Set up a coordinate system for the problem, especially important for more complex 2 and 3 dimensional problems.  You may need to choose a non-cartesian coordinate system:
    1. fixed, inertial (x,y,z) coordinate system (cartesian)
    2. fixed, inertial (r,[theta],z) coordinate system (cylindrical)
    3. other possible inertial coordinate system, for instance spherical
    4. non-inertial coordinate system
  4. Evaluate the forces in your chosen coordinate system, and write down the equations of motion, F = ma .  Remember to include fictitous forces if you use a non-inertial coordinate system, and write down the correct form for a = d2r/dt2if you are using a non-cartesian coordinate system.
  5. Solve the equation of motion.  If the task looks extremely difficult or impossible, consider if it might be easier in a different coordinate system.  Try re-reading the statement of the problem, paying particular attention to your diagram of the problem.  If, after 20 minutes or so, you have made no progress on this problem, leave it and go on.  Come back to it later, perhaps after talking about it with a classmate or the professor.
  6. Re-check your work for missing "-" signs and "factors of 2".
Of course, many problems are different, and don't require you to solve the equation of motion, but instead to apply some other derived results to a specific case.  In these situations, there are often new terms that are used, and you should have a good understanding of what they mean.  It may be helpful to write down a "vocabulary list" in these situations.

Feedback is welcome.  Send your comments or suggestions to  harr@physics.wayne.edu .