## 8 Replies to “AP Physics 1 2015 Free Response Solutions”

1. Don’t you think Q3 on Physics 1 is incorrect, insofar as, the block will not reach 3D since initially the spring is uncompressed at X=0 and then compressed to -D, it will only oscillate between -D <= X <= +D if the surface is frictionless, and if surface on the other side has friction then it will be even less than +D

2. It tells you in the problem the surface is frictionless, and it’s given in the problem that the block will reach 3D when released. I think the question’s OK.

3. Yes I get that the givens are what are given to us, but we know from our physics principles that the block will not reach +3D if it was compressed only -D. I understand what they are trying to ask, and some of my students were baffled by it and asked me whether conservation of energy is violated in the problem, and the answer is YES it is.

• The key to this problem is that the block is not attached to the spring. It is in “contact” with it. Therefore when the block reaches x = 0, there is no restoring force on the block. The block is free to continue moving to the right without the spring acting on it. The block will slow due to friction.

4. How can you know the block won’t reach 3D if it was compressed to -D? That depends upon the spring constant of the spring. I’d assume in a problem like this that the spring constant of the spring is whatever is required to allow the block to extend to 3D when released if it were compressed -D. So you do work on the spring, compressing it to -D, and when released, that becomes the kinetic energy of the block as it reaches x=0, and eventually becomes thermal energy as friction does work on the block until it reaches x=3D.

5. The key to this problem is that the block is not attached to the spring. It is in “contact” with it. Therefore when the block reaches x = 0, there is no restoring force on the block. The block is free to continue moving to the right without the spring acting on it. The block will slow due to friction.

6. The drawing gives you the impression that the block is attached, or at least it does to me. The spring has a horizontal piece extending out to the block, which makes it look like it’s fastened.

I just finished a one year internship to begin teaching physics as a second career. Precision in phrasing and depicting test questions was/is a big challenge for me. (I worked in quality assurance and testing for 28 years, so maybe that doesn’t help).

• Hi Keith — there are a LOT of pieces of the AP-1 and AP-2 exams where the wording / drawing leads to some potentially ambiguous situations, and having recently attended a workshop where grading standards were discussed, I wasn’t thrilled with what I heard. I think these courses have a lot of ‘growing’ to do, and am hopeful those who are in a position to do so are in the process of refining and optimizing the courses.