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Problem Solving Hints

  1. Be sure you understand the question! If you have never seen the situation described, try to mimic it with simple apparatus. Always draw a line sketch of the situation and put on important data; include force and field vectors.
  2. Try to "guess" the answer, at least to the extent of knowing such things as the direction of resultant forces or motion if not the actual numbers. If you cannot guess, you probably do not understand the question.
  3. This is the difficult step: describe the physical situation in mathematical language. If you successfully complete this step the rest is relatively straightforward.
    Determine which physical principles apply in order to know what equations to use. For example, if you have an accelerating body you almost always use F= ma; changing magnetic fields always induce voltages in conductors so use V = -di/dt; if your collision is elastic then you can use conservation of mechanical energy, etc. Memorize and use only the simple equations which result from the basic principles, and not the more complicated equations derived from the basic ones.
  4. Combine your equations algebraically to solve for the unknowns. This often results in a cancellation of terms which greatly simplifies the problem.
  5. Verify the dimensions of your final algebraic expression (e.g., velocity must be in m/s) to check for errors in algebraic manipulation.
  6. Finally, insert numerical values in SI units and calculate your answer. Is it reasonable? For example, a coefficient of friction is usually between 0 and 1; the speed of an object is always less than that of light in vacuum; conservation of energy cannot be violated. If you have no idea if your answer is reasonable, you might try to mimic the physical situation or look up some physical data in a handbook.

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