Which are the most difficult AP Physics B questions, and the Pictorial Index

Drew Austen poses this intriguing thought experiment: Which AP Physics B problems have been the toughest?

My first instinct is to remind everyone that the AP Physics B exam has been of remarkably consistent difficulty over the years.  While sure, some questions have been tougher than others, the variation has been minuscule compared with the variation in textbook problems, most college or high school physics class test problems, or with even AP Physics C problems.

Used to be, back when I was teaching three sections of AP Physics B every year, I could perform a party trick: name a year and a problem number, and I could reliably describe the AP Physics B problem from that exam.  I can't do that off the top of my head any more.  

But I do have a cheat sheet: the Pictorial Index of Previous Exams.  This file includes an inch-square box for each problem on each exam stretching back to 1979.  Each box includes a thumbnail picture of the diagram in the problem stem, and a few words of summary about the problem. 

I first received a copy of this index on CD from Gardner Friedlander, who administers the PGP-secure site.  If you teach AP, get yourself a password to this site.  I can't link you a copy of the Pictorial Index, but look on PGP-secure for B FRpictindex.  There Martha Lietz, an outstanding physics teacher from Evanston, has posted her version.  You can pick up my version by attending an AP Summer Institute.

I use the pictorial index all year long when I teach AP.  I print out a master copy at the beginning of the year. Then when I assign an old AP problem on a test or as homework, I mark off that problem on the index.  I can quickly scan to find a problem on a particular topic; or I can narrow down my search if I want "oh, that magnetism question from 1998, or maybe it was 1999, I don't remember."

Looking at the pictorial index now, I can recall the more difficult questions over the years... these are my own perceptions, based not on the intrinsic difficulty of the topic.  Rather, I call a problem "difficult" if it challenges even students who have a firm grasp of the underlying concepts.

2012 B2 -- two spheres colliding as they hit the ground; symbolic manipulation of conservation of energy and momentum

2011 B2 -- electric field and potential produced by a charged sphere with a metal sphere placed nearby

2008 B3 -- wire-and-magnet experiment on a scale

2006 B2 -- determining when a sprinter stops accelerating

2002 B3 -- 1993 B3, electromagnetic induction including graphs of current and voltage through a wire loop

1995 B3 -- hanging mass inside a loopy roller coaster

You have a different list?  Of course you do... we're doing the AP Physics equivalent of discussing "which was the best Boston Red Sox team ever?"*  There's no right answer, just a pub argument.  Go ahead and throw your choices in the comments section.

* Two possible answers include (a) 1917, and (b) the team with the best steroid provider