2015 AP Physics 1 solutions -- my draft version

The AP Physics 1 exam was five days ago.  Click the link to see the free response questions.  

I solved the problems last weekend.  You may see what I came up with here, via PGP-secure.  This link is teachers only.  Students, if you want to see my solutions, you'll need to ask your teacher for access.  Teachers, if you don't have a PGP-secure account, you should -- instructions are posted on the website.  The site has a humongous volume of fantastic materials for all levels of physics teaching.

What about my thoughts on the exam itself?  Well, it was exactly what we expected.  No explicit calculations.  Lots of explaining.  Three mechanics questions, one circuits question, one waves question.  It will reward students who know how to justify their answers with respect to facts, equations and calculations.  It will destroy students who try to plug random numbers into random equations.

 Problem 1 is a great and straightforward question.  I like the explicit demand that the free body diagram be drawn to scale -- the tensions are equal, and less than the big block's weight, and more than the little block's weight.  Both parts (b) and (c) require an understanding of treating the two or three blocks as a system.

Problem 2 requires that students interpret circuit language.  I'm sure I'll post on this eventually... I began the circuit unit with what I called "nonrigorous" definitions of voltage, current, resistance, and power.  Once we could memorize and calculate using VIR charts, and once we had plenty of experimental experience, we learned the AP language:  energy per charge is voltage or potential difference, energy per time is power, charge per time is current.  If my students made these connections, they should have done just fine.  In fact, I even did that same experiment in class in January where we see whether a bulb is ohmic or not.  I can't guarantee that my students remembered the experiment, but...

Problem 3 is somewhat improved over previous attempts at the qualitative-quantitative translation.   I like that there was only one student's reasoning to deconstruct.  My class said they felt like they were repeating themselves over and over -- the distance square term in the spring energy equation means that doubling the distance compressed quadruples the energy stored.  As long as they followed directions, and made explicit reference to their equations and what those equations mean, they will hopefully be fine.

Problem 4 should have been seven free points for all.  In fact, we are giving this problem to our regular 9th grade conceptual physics class to see how they do.  We think they'll ace it.

Problem 5 is my favorite.  It's basically a violin -- you have to use different gauges of string in each of the strings on a violin.  I love the "will the graph be linear" question.  And the last question simply asked to locate the antinodes; once again, students had to interpret AP Physics 1 language, but the released materials have been pretty clear that "average vertical speed of a point on the string" is something students are expected to understand.

Remember, my solutions are unofficial, and may even be incorrect.  I guarantee that I would have gotten a 5 on the exam, but not that I get 100%.  I don't know how the grading will work (yet), either -- perhaps some of my phrasing won't earn full credit.  We'll find out in a few weeks.

GCJ