# Problem Solving Hints

**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.
**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.
- 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**= m**a**; 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.
- Combine your equations algebraically to
**solve for the unknowns**
. This often results in a cancellation of terms which greatly simplifies
the problem.
**Verify the dimensions** of your final algebraic expression (e.g.,
velocity must be in m/s) to check for errors in algebraic manipulation.
- 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.