Introductory / 100 level -- No math
No calculus / 200 level
Freshman physics major, calculus may be required
Sophomore physics and above
Junior physics and above
Graduate
The dot by each problem's menu entry roughly indicates the level of student it's geared toward
Introductory / 100 level -- No math
No calculus / 200 level
Freshman physics major, calculus may be required
Sophomore physics and above
Junior physics and above
Graduate
How much of the dot is showing gives an idea how involved a problem is or how much work you'd need to do to solve it:
" Back of the Envelope " -- Hardly any work
General " Pain in the Posterior Problem " -- Lots of algebra/parts
Of course, these marks are very subjective, and there is certainly some overlap between the different levels (especially the first 3). A student in Physics 201, for example might be able to do some of the " quarter dot " or " half dot " problems in the next level, and at the same time have trouble with some of the problems in the introductory level. More than likely, though, they won't be able to deal with any of the graduate level problems...
You are encouraged to use your own judgement, if you run into a problem you can't do, then you know what you need to learn. Also, don't be discouraged by problems labeled as being more difficult. Oftentimes these are the most fun and satisfying problems to do, and more than likely have been taken from real life.
dmason@zebu.uoregon.edu