The question in question asked about a cart on a long, bumpy track. Specifically, it demanded a sample velocity-time graph for the cart as it crossed several bumps; then it asked what should happen to the cart's speed in between bumps if the angle of the track or the distance between bumps changed.
I heard from and about a number of teachers who complained. What kind of crazy-arse experiment is this? No one does this in their class. Ridiculous. The AP Physics 1 exam has jumped the shark already.
My reaction to this question was, "Cool, what a great experiment, I wonder if I could set this up in the laboratory?" And this week, Zach Widbin did set it up.
Zach's teaching in Phoenix, but he's from New York, so he attended my summer institute in Mahopac, NY. On the last day of the institute, teachers spend a couple of hours playing in lab, setting up experiments that they can share and use in their own classes.
He inclined a PASCO two-meter track by two degrees. He wrapped rubber bands around the track at 40 cm intervals, providing the bumps -- see the picture at the top. The cart was a PASCO smart cart, which sends velocity-time data to an ipad via bluetooth. The velocity-time graph is to the right.
The original question asked what the graph should look like... but also, what should happen with a steeper incline? With a larger space between bumps?
Well, Zach checked those things out, too. The steeper incline gave a faster max speed. He did smaller bump spacing, and got a smaller max speed.
The AP question itself postulated a very long track, with 100 bumps. Zach only had a few bumps. But there's no reason we couldn't tie together several of these two-meter tracks and try this again. In fact, PASCO makes modular 50-cm plastic track pieces which can fit together in as long or short a string as you'd like. Someone who has access to a wood shop (or, for those who prefer sexy terminology, a "maker space") could get a long plank, and then drill bumps into the surface. Zach's approach isn't the only way to go - it's the one-morning-at-an-institute version. I'd love to see pictures of your own setup.