How to solve physics problems?

  1. Draw a diagram, if at all possible, even if it is so simple-minded as to seem silly. Only when you have worked a given type of problem so often that you automatically draw a mental diagram you can stop drawing one on paper.

  2. Read the problem carefully, listing all quantities given and requested. (Leave room for more quantities you may need later).

  3. Play with the situation either mentally or with models. Try to understand the behavior of the system qualitatively. Look for simpler special cases (zero angle, 90 degree angle, a zero length, a large mass, etc.) where the answer to the problem is obvious.

  4. Decide what kind of problem you are working on (response to a force, energy conservation, equilibrium, or what have you). Use examples from your notes and text to help with the decision and with the general techniques used to solve problems of this type.

  5. Determine whether or not the data given are adequate. If not, decide what is missing and how to get it. You may need to look up some standard constant in a table.

  6. Work on the algebra to reduce the number of unknowns. When you have the same number of relevant, independent equations as you have unknowns, you probably have enough equations.

  7. If necessary, add to your list of quantities any additional ones which you can compute but which were not asked for. Sometimes these additional quantities are needed to finish the problem.

  8. When you have an algebraic solution, put in numbers WITH UNITS. Be sure that all your numbers are in consistent units.

  9. CHECK

    P lausibility [Algebra OK, numbers reasonable, signs correct?]
    U nits [Are all consistent and appropriate?]
    N otation [Vectors shown?]
    S pecial cases [Does your solution obey those from step 3? If not, why not?]

  10. When everything seems to be correct, write out a complete, logical solution. Watch for the correct number of significant digits in the numerical answers.

  11. On homework problems, outline the method of solution in 2-3 lines or practice working through the solution quickly. If a similar problem occurs on an exam, you may have less time to think than you would like.