Outline of Strategy for Solving a Physics Problem



Outline of a Strategy for Solving a Physics Problem

1. Restate the problem in your own words. Write it down! Fill in the blank: “I want to find ______ .” What is the answer supposed to be? A time? A distance? An energy? What are its units?

2. If appropriate (most of the time it is!), sketch a diagram of the situation.

3. List the known quantities, their symbols, their numerical values and their units. Label these on the diagram, also.

4. Ask yourself what other information is given in the question that might relate the unknown to the known quantities? THINK about what physics concept(s) might have to be applied!!! In some cases, the physics concept may be implied rather than stated explicitly. For example: Is there constant acceleration? Is there energy conservation? Is there momentum conservation? Do you need to use one of Newton’s Laws? ….

5. The needed concepts should lead you to equations which involve your knowns and unknowns. If you can, write these down. Also, write the name of the physics concept you are using on your paper, next to the equation that you have. If you are stuck, think again about how the known information is related to what you are seeking. Do the knowns seem related to some important Law, Principle or Rule? If so, then that’s what you need! Without this, you can’t proceed. (Example: A question involving forces should lead you to consider Newton’s Laws.)

6. Use words and sentences to explain what you are doing, and what the equations mean. Check to make sure that these really apply to your problem.

7. Check your equations! Can you use them to solve for the desired quantity? If so, then do so using CAREFUL algebra. Try to get the desired symbol on the left hand side of the equals sign, and all other symbols on the right hand side.

8. ONLY NOW (the 8th step!!) should you substitute the numerical values of the knowns (with their units!) in place of the symbols for the knowns. Check that the units will combine to give the proper units for the unknown you are looking for. ONLY NOW should you punch in the numbers in your calculator. [Also check to see if some unit prefixes can be cancelled. If so, it could speed up your calculation. Using all SI units also may help.]

9. Round off the answer to the correct number of significant figures, then write it down, (with units!) and sketch a box around it. If your answer has a very large or a very small numerical value, PLEASE use Scientific (power of 10) Notation! (On exams, I will take off some points if you don’t use this notation for very large & very small numbers!!)

10. You are almost finished!! Check again to see that you really answered the stated question. Look at your answer and THINK about whether it makes any sense! Does the size of your answer seem reasonable? Or is it ridiculously large or small? Is it negative when you were expecting a positive number, or vice-versa? Or is a negative value OK if you interpret the result correctly?

If you couldn’t solve the problem, try to understand why. You were probably missing some important concept (see steps 4 and 5 above). If you can’t get anywhere, formulate a question or two. Write these down. Then, ask your TA or me about it.

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