Yesterday, I took the free-response portion of my physics final. I followed Abraham (peef2)’s advice and looked around the directories UCCP (University of California College Prep) had online — and unprotected
Yes, the physics final and answers were all there. I decided to look at the answers (yesterday — yes, after the test) after Joey pointed out to me that at least one of the problems are not only grammatically incorrect, but also factually incorrect.
I checked with my knowledge (and the book’s for confirmation), and found that in the key, the answers of 5 of the 12 free response questions were wrong. I will briefly explain them. (Click here for the final questions, answers and explanations for both the MC and the FR — yes, I did steal/”hack” this from UCCP, but it’s their fault)
1. Let’s start with the first one. Yes, the very first question you encounter is wrong. I can’t believe UCCP went through an intermediatary step of using pi as a rational number and multiplying it. If it were smart enough and used proportions, the answer would have come out to be 1.69 m/s, not 1.68. (That’s the problem with too many mathematical steps — loss of accuracy). I know a 0.6% error does not seem all that big, but I’ve seen Mr. Monsees take points off of my quizzes for errors with HIS accuracy.
4. I was quite relieved when I found that the next consecutive 2 questions were all completely correct! Well, as you can tell, my hopes were too high. When I reached #4, I was astounded by the error UCCP made. It wasn’t something minute or stupid like #1 — this one was huge.
The question reads: A closed organ pipe has a length L = 70.0 cm. The speed of sound is approximately 340 m/s at 20° C, and increases by approximately 0.6 m/s for each degree C. What is the fundamental frequency f1 of the pipe if the air temperature is 0° C?
Obviously the first step would be to find the speed of sound at the required temperature. UCCP’s explanation had: v0 =(340 m/s)−(0.6 m/sâ‹… deg)(20.0°)= 322 m/s. This here is where the problem lies. 340-0.6*20 = 340-12=328, not 322. Since when did 340-12 = 322? This looks like the type of subtraction Ms. Jankowski would make (:P), but that is absolutely forgivable because she teaches English — and she is definitely competent in that field — whereas Mr. Monsees “teaches” Physics. Physics requires mathematics, and something as simple as 340-12 should not be evaluated incorrectly.
As a corollary to the above, the obtained answer is incorrect.
6. Another fundamental mistake was made by UCCP in this problem. The question required the calculation of the Carnot efficiency, which must be calculated using absolute temperatures, meaning in Kelvin, not Celsius. The explanation directly plugged in the given temperatures in Celsius to the efficiency “formula”, and used that to determine the answer — which is wrong, because Celsius is not absolute. Needless to say, that was a fatal error.
7. I was somewhat scared when I saw two questions wrong in a row. But this question is relatively simple. Basically we are to find the value of a variable given the value of the other one. The question reads: A galaxy is observed to be moving away from our galaxy at a speed of 22 km/s. How many light-years away is the galaxy? We just need to use v=H0d, and solve for d.
The explanation plugged in 26 km/s in place of 22 km/s for v. Fatal mistake eh? The answer was off by around the same proportions.
10. This question was also extremely easy, like the above. Just solve for a variable given the value of the other ones. The question is: The pressure on the surface of a research submarine is 2.0×107 Pa. The submarine has one window with a diameter of 30 cm. What is the total force exerted on the outside of the submarine’s window? We use the formula P(pressure) = F(force)/A(area), and solve for F=PA. UCCP made the same mistake as above. It substituted in 1.8×107 Pa in place of 2.0×107 Pa.
I mean, I thought about accounting for atmospheric pressure inside the sub, but that would only make it 1.99×107 Pa (which rounds to 2.0×107 Pa in 2 significant-figures), not a significant difference since the end result is in 2 sig-figs. And there isn’t any other force that would somehow decrease the pressure on the sub by 20 atmospheric pressures. It’s just insane.
Yes, the given answer was wrong.
Considering there are only 12 FR questions, and 5 are wrong on the key, what can we say about UCCP?
I will rant about MC after I take a look at that in more detail.