Random Collection of Observations
Last year, on the first physics exam, I had about 65% of students answer correctly when asked about the sign and direction of the acceleration for an object in free-fall, both on the way up and the way down. (Big Big correction: Last semester, only 30% of my students answered both correctly. 65% last semester gave either both correct OR incorrect in a way that implied negative acceleration meant slowing down.)…
This year, one of my standards specifically addressed this, and there are no surprises. This year, with very similar questions, 93% of my students got the two questions correct. The students who didn’t get it right, chose not to re-assess after an initial unsuccessful attempt.
So those two questions were very similar to the standard. A harder and less similar question was about making sense of what an acceleration of – 2.7 m/s/s tells us. Students had to choose a correct statement about the motion from a list of option. The right answer to choose was that there is not enough information to tell whether its speeding up or slowing down. On this question, 70% of the students got that answer correct, with the two most common wrong answers being that it’s slowing down and that it’s moving at constant speed.
Looking to the open-ended problem with free-fall, 100% of students chose the correct direction for the acceleration due to gravity in the problem and 0% of students tried to solve for acceleration as if it were unknown in free-fall. I don’t know exactly how many students did this last year, but it was significant enough for me to notice.
On another note, I did not have any standards for interpreting graphs, and students did poorly on a simple question about a position vs. time graph. Many of them, I suspect, were simply remembering an answer from a practice test where it was a velocity vs time graph. It was the same question about where does the object change direction.
Most recent update:
The sign for acceleration due to gravity on the way up and down: 93% vs. class average of 66%
Whether negative acceleration means slowing down: 70% vs. class average of 42%