Ah, it's good to be able to download the questions 48 hours after the exam again. It's good to be back to five total questions, two long and three short. We're back to something approaching normal in the AP Physics 1 world!
Big thanks to the College Board for the format of the test question download (available here). Note that there's space for students to answer each question! For the first time on 25 years of teaching AP Physics, I don't have to spend time cutting and pasting.
Anyway. Here are my solutions to the exam. This file is accessible to TEACHERS ONLY through the "pretty good physics - secure" site. If you're a student and want access, ask your teacher to join pgp-secure using the instructions on the site. There's no point in pretending to be a teacher - the folks in charge check membership requests carefully, and they will take away your birthday if you're not actually a teacher.
I loved these questions, as has been typical for a while. The AP Physics 1 development committee is in a nice groove in which the problems are predictable in style but unpredictable in content. Awesome.
For number 1, it's much easier if you've memorized the "range equation" for kinematics. My students haven't; but no worries, it's still doable, just requiring an extra step of algebraic kinematics. No trig identities necessary for credit!
The experimental question required essentially no physics content knowledge, only experimental skills. (Graphical analysis is an experimental skill!) Fantastic! No free points for writing or deriving equations, just for doing and analyzing results from a lab. Cool.
The paragraph question was clever and - for those who understand energy conservation well - straightforward.
For number 5, the wording is important! They're not asking for the AP Physics C-level three-body problem with a massive pulley. They want the net torque on the objects-pulley system. So the only external force is that of the earth. You can use mg*lever arm to find each torque. Then parts b and c are similar to the problem I did in my very first AP live show in 2020, back when Edna wasn't even wearing her bow!
As always, I guarantee I got a 5, but not that I got a perfect score. Send me your thoughts!
Hey greg! My solutions are nearly identical. The only difference I saw is in the experimental design. Having done the ED problem at the reading 2 years ago, we gave 2 points for repetition - one for repeating each trial multiple times, and one for using all of the "scenarios" (in that case, spring launcher at 3 pin lengths). So for this, I said to test/break multiple rods of the same thickness, and then repeat for the rods of other thicknesses. I'm curious if "reduce uncertainty" will explicitly ask for multiple breaks of each type of rod, or if using a force probe (making a F vs t) for just one rod of each thickness graph will be sufficient.
ReplyDeleteDan, I don't know the answer to that. It depends on who the table leaders and question leaders are, and what they decide.
ReplyDeleteIf it were my question - I've graded more experimental design questions than anyone, but I haven't done one since 2016 - I'd assign one point for somehow reducing uncertainty. To me, though, making a graph of Fmax vs radius for all available thicknesses is sufficient, because it's a graph on which we can look at a best-fit line (or curve). The point is to take as much data as possible. But it's more important to me to explore the parameter space - measure Fmax for every possible thickness - than it is to hone in on the error bar for one point on the graph.
This is my philosophy as a scientist and as a very experienced experimental physics teacher. Those with a statistics background may argue with me. I'm not so interested in knowing what is required for publication, or what is the absolutely most optimal method. If you're thinking about "standard deviation" than you're not thinking at the AP Physics 1 - level. :-)
I'm interested in what is generally reasonable to expect in a first-year physics lab. That's more than just "divide Fmax by the radius and see if you get the same number", but less than "we've included error bars at the 2-sigma confidence interval with an R^2 value of 0.95, whatever that means."
I found it interesting that the students had to generate a graph in all five questions, which I haven't seen in previous years. My students are taking Administration 3 of the exam, and I had them do these FRQs as a practice test. I had one student draw the graph in Question 4 with a very slight downward slope instead of a horizontal line between L0 and 2L0, with her argument being that no object in the real world could just roll forever... there would still be a gradual loss in mechanical energy over time. I can't argue with her point, but I wanted to know if you thought she might possibly still get full credit? She didn't actually write this on the test... she just told me after I docked her a point for not having a horizontal line. What are your thoughts?
ReplyDeleteDrew, I'd tell her: sure, no object can just roll forever. But, an object within my classroom can very easily roll such that the velocity-position graph generated by a smartcart will be horizontal. A cylinder on an incline in the classroom does not constitute "forever". And physics 1 is all about making simplifying assumptions, about recognizing how experiment *is* the "real world".
ReplyDeleteThis problem didn't ask about "forever." It asked about a cylinder on a track, for a distance similar to the distance along the incline. Further argument about "forever" constitutes lawyering up. :-)