Good morning. I have already made videos for Qualitative/Quantitative Translation,
Paragraph Argument Short Answer, and Experimental Design Questions. This is about the generic
“Short Answer” type of question for AP Physics exams. According to the AP Physics 1 Course and
Exam Description, 2 out of the 5 free response questions on the exam will be this generic “Short
Answer” question type. And, even though 40% of the free response questions will be “Short Answer”,
the Course and Exam Description only has, as far as I can tell, the following to say about
"Short Answer” questions. Billy? ♪ Flipping Physics ♪
“The two short answer questions focus on practices and learning objectives
not focused on in the other question types.” Well, that’s not very helpful.
All that tells us is that “Short Answer” questions cover everything not covered in the
Qualitative/Quantitative Translation, Paragraph Argument Short Answer, and Experimental Design
Questions. Right.
Agreed. So, in order to figure out what “Short Answer” questions really are, let’s look at the
10 “Short Answer” questions which are in the publicly released AP Physics 1 exams from 2015
to 2019. When you go through those 10 “Short Answer” questions, you will discover that a full
5 of them are about topics which, in December of 2020, were removed from the AP Physics 1
curriculum. That’s right, 50% of the publicly released AP Physics 1 “Short Answer” questions
are about physics topics which are no longer a part of the AP Physics 1 curriculum.
That means we only have 5 “Short Answer” free response questions to analyze to understand what
“Short Answer” questions for AP Physics 1 are. One free response question from each year. I
already have detailed solution videos for each of these free response questions
and each of those solution videos also includes suggestions on how to score better on the exam,
therefore, I think it will be useful here to look at all 5 of them in a general sense to find
out what “Short Answer” questions are. The five free response questions we are going to analyze
are 2015 #1, 2016 #1, 2017 #4, 2018 #1, and 2019 #1. Each short answer question is worth 7 points.
That means there are a total of 35 points represented by these free response questions.
3 out of the 5 free response questions, 2015 #1, 2016 #1, and 2018 #1, each have a free body
diagram which is worth 2 points. That means, 6 out of 35 points, or roughly 17% of all the points
available in these 5 free response questions come from simply drawing free body diagrams correctly.
And one of these free body diagrams, 2018 #1, only had 1 force in it, even though it was worth
2 points. Please take your free body diagrams seriously. Actually, let’s
look at one free body diagram specifically. Bobby, please read, from the 2015 AP Physics 1 exam,
question number 1 through part (a). “Two blocks are connected by a string
of negligible mass that passes over massless pulleys that turn with negligible friction,
as shown in the figure. The mass m 2 of block 2 is greater than the mass m 1 of block 1.
The blocks are released from rest. Part (a), The dots represent the two blocks. Draw free-body
diagrams showing and labeling the forces (not components) exerted on each block. Draw the
relative lengths of all vectors to reflect the relative magnitudes of all the forces.”
Thank you Bobby. Bo, please draw the free body diagrams.
Sure. Well, both blocks have a force of gravity acting down on them.
Call them force of gravity 1 and force of gravity 2. Oh, and make the arrow for force of gravity 2
longer in length than the arrow for force of gravity 1 because mass 2 is greater than mass 1.
And each mass has an upward force of tension acting on it because both are being
pulled upward by a string. You can call them force of tension 1 and force of tension 2.
And, because they are two ends of the same string and both pulleys are massless and frictionless,
those two forces of tension are equal in magnitude and need to have the same length
arrow. That is the complete free body diagram. Correct, a couple of quick things to point out.
When you can, you should estimate the relative lengths of your free body diagram arrows. And
you should never break forces into components on a free body diagram you are drawing as an
answer in a problem on an AP exam. And please, definitely do not add forces to your free body
diagrams simply because you do not feel there are enough forces in the diagram.
And now, class, after you draw the free body diagram on a problem,
typically what should you do next? Sum the forces!
Break forces into components, redraw the free body diagram, and then sum the forces.
Right. Yeah. If you need to, break forces into components
and redraw the free body diagram somewhere other than where you drew you're answer to the problem.
And then you will likely use Newton’s Second Law to sum the forces at least once, and sometimes
you need to sum the forces twice in two different directions which are perpendicular to one another,
and then manipulate the equations to solve for a variable. You can see how we did that in the
problem we were just talking about. We identified the positive direction,
summed the forces in that positive direction, and solved for the acceleration of the 2-block system.
Summing the forces and manipulating equations to solve for a variable is what needs to be
done on all 3 of the free response questions which ask you to draw free body diagrams.
Those solutions on the 3 free response questions are worth a total of
8 out of 35 total points or roughly 23% of all the points. In other words,
drawing free body diagrams and summing the forces accounts for a total of 14 out of 35 points
or 40% of all the points on the 5 publicly released “Short Answer” questions. Again, I say,
please take your free body diagrams seriously. Absolutely. Okay. Sure.
Thanks. But, the largest category of points on these 5 “short answer” free response questions
is where they present you with a situation, ask you to answer a multiple-choice question,
and then justify or explain your answer. 15 out of 35 points, or roughly 43% of all the points
fit in this category. Every one of the 5 “Short Answer” free response questions has at least
2 out of 7 points for a multiple-choice question and answer justification. In fact,
all 7 points of AP Physics 1 2017 #4 fit in this category. And several free response questions have
a part worth only 1 point which fits in this category, which means what really matters for
these is your justification or explanation, not the multiple-choice answer itself.
Many of these questions make a change to the situation first presented, and then ask you
a multiple-choice question about how a variable will change, and ask you to justify your answer.
For example, Bo, please read part (c) of the free response question we’ve been looking at.
“Block 3 of mass m 3 is added to the system, as shown. There is no friction between block
3 and the table. Part (c), Indicate whether the magnitude of the acceleration of block 2 is now
larger, smaller, or the same as in the original two-block system.
Explain how you arrived at your answer.” Notice how they have changed the original
physical situation and asked you to answer a multiple-choice question about how a variable
changes. In this case they have added a block and asked you how the acceleration of block 2
will change with the addition of that third block. And, again, the most important part, is where you
“explain how you arrive at your answer.” Please realize that. These questions are really about
you using words to explain the physics behind your reasoning to answer the multiple-choice
questions. The last category I identify is the 5 points from part (a) of AP Physics 1 2019 #1.
Here they present you with a situation of 2 objects which collide
and ask you to graph the speed of the center of mass of the system as a function of time.
Your entire answer to part (a) is worth 5 points, is only the lines you draw on the 5 parts of
the graph. No explanation necessary. 5 out of 35 points, or roughly 14% of all the points on these
5 “Short Answer” questions are for drawing a graph with no explanation necessary. So, please realize,
the College Board may throw something completely different at you and you need to not get
discombobulated by that. Dis…combobulated?
Yes, do not get discombobulated by a type of question you have never seen before on an AP exam.
Honestly, if I were writing the exam, I would try to present you with something
new to test your understanding of the physics rather than pattern recognition of past exams.
Yep. He would do that. Yeah.
Lastly, there is a complete lack of numbers in all 5 of these “Short Answer” free response questions.
Everything is free body diagrams, setting up equations, variable manipulation,
graphs, and understanding and explaining how variables will
be affected by changes to the physical situations presented.
Whenever you are manipulating equations, you are manipulating variables not numbers. As I have said
so many times before, you need to let go of your numbers dependency. Also, if you want to see the
specifics of how I categorized the different parts of the 5 “Short Answer” free response questions,
I put those in the lecture notes on my website. Link in the description. Alright,
that is what I have to say about “Short Answer” questions on the AP Physics exams. Best of luck
on the exams. Thank you very much for learning with me today, I enjoyed learning with you.