Physics I Homework Standards

Problems are  assigned twice weekly from the textbook or from separate notes.  In order to adequately evaluate students' solutions to homework in a timely fashion, certain standards are necessary.  If these standards are not followed, the resulting problems may not be graded and the student will lose credit for completing the homework.

1.  The problem solution must be "self-contained", i. e. the nature of the problem must be indicated.  It is best to explain the problem in your own words.

2.  The solution should be developed by invoking the primary physical laws, writing the appropriate (easy to remember formula) from the physical laws involved.

3.  The solution should be solved algebraically before any numbers are inserted.  This saves a lot of work.  It is much easier to write the symbol for density than to write the numbers, including the powers of 10.  It is much easier to manipulate the symbols for the quantities with the rules of algebra than to manipulate the numbers.

4.  Save "plugging-in" the numbers for the last step.  This saves writing gobs of numbers and it minimizes errors.

5.  Box or highlight the final answer, including the correct units propagated from the formula, and display the correct number of significant digits.

6.  The handwriting must be legible!  The graders will not waste time trying to decipher illegible scrawl.

Here is an example from a typical textbook:

2.  A major motor company displays a die-cast model of its first automobile, made from 9.35 kg of iron.  To celebrate its hundredth year in business, a worker will recast the model in gold from the original dies.  What mass of gold is needed to make the new model?  The density of iron is 7.86 x 103 kg/m3, and that of gold is 19.3 x 103 kg/m3.

Good solution:

The problem question has been re-written in own words.

The given information is clearly displayed with appropriate symbols.

The formula based on fundamental definitions is clearly displayed.

The technique for solving (notably that the volumes are equal) is clearly displayed.

The solution is first solved with the algebraic symbols in a formula, then the numbers are "plugged-in" to obtain the numerical answer.

The numerical answer is displayed with the correct significant digits and units and the answer is boxed.

An interesting sideline is entered (not necessary, but it shows some realistic insight)!

Bad solutions: 

Besides the lack of showing the calculations or formulae used in the solutions shown below, there are other faults.

Only the answer is displayed, the problem is not outlined in sufficient detail.

Incorrect regarding significant digits.

Answer not boxed or highlighted.

Formula not shown with algebraic symbols.
Units missing from the calculation.
Excess digits in the answer by copying all 11 calculator digits!  This is the most egregious error!

Error in the numbers as well as a power of 10.  Student should realize that the answer is ridiculous.  The model made from gold should be considerably more massive than the iron model.