AP Physics C: Mechanics
How to Approach the
Multiple-Choice Section
General Preparation
Information Allowed / Not
allowed
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No Calculator – you don’t need to use
a calculator to answer the multiple
choice questions
No Formula Sheet – you will be tested
over your ability to use the formulas,
thus you should know the formulas.
Easy Calculations
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What kinds of questions will be asked
on the multiple choice section?
Designed to test your knowledge of
formulas
Easy Calculations Example
A ball is dropped from a 45 m high platform.
Neglecting air resistance, how much time
will it take for this ball to hit the ground?
a)
b)
c)
d)
e)
1.0 s
2.0 s
3.0 s
4.0 s
5.0 s
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Easy Calculations Example
A ball is dropped from a 45 m high platform.
Neglecting air resistance, how much time
will it take for this ball to hit the ground?
a)
b)
c)
d)
e)
Planet X is twice as massive as Earth, but
its radius is only half of Earth’s radius. What
is the acceleration due to gravity on Planet
X in terms of g, the acceleration due to
gravity on Earth?
a)
b)
c)
d)
e)
¼g
½g
g
4g
8g
Designed to test your understanding of
the size of things, measurements, or
just numbers.
Proportional Reasoning Example
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Designed to test your knowledge of
how to use equations, except that you
don’t have to plug in numerical values
to solve them.
Proportional Reasoning Example
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1.0 s
2.0 s
3.0 s
4.0 s
5.0 s
Proportional Reasoning
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Order of Magnitude Estimates
Planet X is twice as massive as Earth, but
its radius is only half of Earth’s radius. What
is the acceleration due to gravity on Planet
X in terms of g, the acceleration due to
gravity on Earth?
a)
b)
c)
d)
e)
¼g
½g
g
4g
8g
Concept Questions: “WHY?”
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These are designed to test your
understanding of vocabulary and
explanations for physical phenomena.
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Concept Questions: “WHY?” Example
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At a smooth, sandy beach, it is observed that the
water wave fronts are traveling almost perpendicular
to the shoreline. However, a helicopter pilot notices
that several hundred meters away from the shore,
the wave fronts are traveling at about a 45° angle to
the shore. What is a possible explanation for the
change in the direction of the water wave fronts?
a)
b)
c)
d)
e)
These ask you a simple question
based (obviously) on a diagram.
Direct Solution with Variables Example
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A pendulum of length L is drawn back to position P, as shown
in the above diagram, and released from rest. The linear
distance from P to the lowest point in the pendulum’s swing is
d; the vertical distance from P to the lowest point in the swing is
h. What is the maximum speed of this pendulum in terms of the
above variables and fundamental constants?
a)
d)
2 gd
2 gL
L
b)
e)
2 gd
c)
•
At a smooth, sandy beach, it is observed that the
water wave fronts are traveling almost perpendicular
to the shoreline. However, a helicopter pilot notices
that several hundred meters away from the shore,
the wave fronts are traveling at about a 45° angle to
the shore. What is a possible explanation for the
change in the direction of the water wave fronts?
The water waves have a greater speed near the shore.
The water waves have a smaller speed near the shore.
The water waves have reflected off of the shore.
The acceleration due to gravity is greater near the shore.
The acceleration due to gravity is smaller near the shore.
Concept Questions: Diagrams
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Concept Questions: “WHY?” Example
2 gh
2 gh
L
a)
b)
c)
d)
e)
The water waves have a greater speed near the shore.
The water waves have a smaller speed near the shore.
The water waves have reflected off of the shore.
The acceleration due to gravity is greater near the shore.
The acceleration due to gravity
gravity is
is smaller
smaller near
near the
the shore.
shore.
Direct Solution with Variables
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Because the AP writers can’t ask you
to do any kind of difficult number
crunching on the multiple choice
section, often they will ask you to do
your problem solving using variables
only.
Direct Solution with Variables Example
•
A pendulum of length L is drawn back to position P, as shown
in the above diagram, and released from rest. The linear
distance from P to the lowest point in the pendulum’s swing is
d; the vertical distance from P to the lowest point in the swing is
h. What is the maximum speed of this pendulum in terms of the
above variables and fundamental constants?
a)
d)
2 gd
2 gL
L
b)
e)
2 gd
c)
2 gh
2 gh
L
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Skipping Questions?
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You earn 1 point for each correct answer
You lose ¼ point for each incorrect answer
You neither gain or lose for blank answers
Thus, if you have no clue, it might be best to
leave the question blank.
If you are able to reduce the number of
answer choices (check for correct units)
then guessing might help you.
How to Approach the
Free-Response Section
Multiple Choice Final Advice
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What do the graders look for?
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Free-Response Tools
You can use most calculators on the
free-response section of the exam.
– Check and make certain that your
calculator is an allowed type. You don’t
want any surprises on the day of the
exam.
Before looking at any student papers,
the graders set a Rubric (a grading
guide) for each question. This includes
what is expected for partial credit and
full credit to be awarded.
Free-Response Tools
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Know your pace. Know your strengths and
weaknesses.
Multiple-choice questions do not necessarily
start easy and get harder. Thus, if you are
stuck, skip it and come back. There may be
easier ones further in the test.
The AP authors know the time limit. They
will not write a problem that really takes 3-4
minutes to solve. Thus, look for the easy
problem approaches.
You will also be allowed to have the formula
sheet for this section of the exam.
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You should have most of these formulas memorized,
but you may use the formula sheet to make certain you
remember the equation correctly.
You may also use the formula sheet to jog your
memory on a particular equation.
Beware: The formula sheet
sheet can
can be
be dangerous.
dangerous. Don’t
Don’t
randomly start searching the formula sheet for formulas
that “look
“look like
like they
they might
might work”.
work”.
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Free-Response Advice
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Always show your work (neat is a plus)!
If you are unsure exactly how to solve a
problem, explain your thinking process to
the grader. You might be able to get several
points of partial credit for your physics
thought process.
Keep your answers succinct (don’t write a
book).
ALWAYS remember units if they are
appropriate.
Free-Response Advice (cont)
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If you make a mistake, cross it out. If your
work is messy, circle your answer. Make
sure the AP readers know what to grade
and what to ignore.
If you get stuck on one question, try
another. Question 3 might be easier than
question 2. Get the easy points first, then try
to get the harder points if you have time.
Free-Response Advice (cont)
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If you don’t know how to solve part a, but
know how to solve part b and it involves
part a’s answer, you can:
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–
Make up a reasonable answer for part a then
use it to calculate part b.
Set some variable equal to the answer from part
a, write a short note (“let v be the velocity found
in part a”). Then solve in terms of that variable.
Free-Response Advice (cont)
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Lab Questions
It may be helpful to include a drawing or a graph in
your answer to a question, but make sure to label
your drawings or graphs so that they’re easy to
understand.
No free-response question should take you more
than 15 minutes to solve. They’re not designed to be
outrageously difficult, so if your answer to a freeresponse problem is outrageously complicated, you
should look for a new way to solve the problem, or
just skip it and move on.
Lab Questions
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Each free response section will
contain at least one question that
involves experiment design and
analysis.
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Steps to Answering Lab Questions
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Follow the directions
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There is no single correct answer.
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Most of the lab questions are open-ended.
There might be four or more different correct
approaches.
Don’t try to “give them the answer they’re
looking for.”
Give them an answer that makes sense – you
might be right.
Steps to Answering Lab Questions
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This sounds simple.
When the test says “Draw a diagram,” it means
they want you to draw a diagram.
When the test says, “Label your diagram,” it
means that they want you to label your diagram.
Yes, you will earn points for these easy steps.
Steps to Answering Lab Questions
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Steps to Answering Lab Questions
Don’t over-think the question
– They’re normally not too complicated.
– Remember, you’re supposed to only take
10-15 minutes to write your answer.
– You’re not exactly designing a subatomic
particle accelerator.
Use as few words as possible.
– Answer the question, then stop.
– You can lose credit for an incorrect
statement even if the other 15 statements
in your answer are correct.
– KEEP IT SIMPLE!
Steps to Answering Lab Questions
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Don’t assume you have to use all the
stuff they give you.
– It might sound fun to use a force probe
while determining the index of refraction
of a glass block, but, really! A force
probe!?!
Steps to Answering Lab Questions
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Don’t state the obvious
– You may assume that all basic lab
protocols will be followed.
– There’s no need to tell the reader that
you recorded your data carefully, nor do
you need to remind the reader to wear
safety goggles.
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