problem_solving in physics

AP Physics Rapid Learning Series - 03
© Rapid Learning Inc. All rights reserved. - http://www.RapidLearningCenter.com 1
Rapid Learning Center
Chemistry :: Biology :: Physics :: Math
Rapid Learning Center Presents …Rapid Learning Center Presents …
Teach Yourself
AP Physics in 24 Hours
1/42 *AP is a registered trademark of the College Board, which does not endorse, nor is
affiliated in any way with the Rapid Learning courses.
Problem Solving inob e So g
Physics
Physics Rapid Learning Series
www.RapidLearningCenter.com/
© Rapid Learning Inc. All rights reserved.
Wayne Huang, Ph.D.
Keith Duda, M.Ed.
Peddi Prasad, Ph.D.
Gary Zhou, Ph.D.
Michelle Wedemeyer, Ph.D.
Sarah Hedges, Ph.D.

Learning Objectives
When to follow problem-
solving techniques
By completing this tutorial, you will learn:
solving techniques
A general problem-solving
technique
How to solve word problems
How to prepare for an exam
Tips for taking exams
3/42
Tips for taking exams
Concept Map
experimental science
Physics is an
experimental science
Requires
Previous content
New content
ExperimentationExperimentation Conclusions
Results &
Conclusions
CalculationsCalculations
Leads to
Often requires
Problem Solving
Requires
Requires
4/42
General
problem-solving
strategy
KUDOS
method
Exam prep &Exam prep &
Exam taking
TipsFor word
problems
Use On Exams

Problem-Solving
5/42
What is Problem Solving?
You are
here
A “problem” is
when you don’there
Problem
Solving
Strategy
when you don t
know how to get
from here…
6/42
You need to
get there
to there

Why is it Important?
Problem solving is needed in every aspect of
physics:
Labs & investigations
Practice problems
Exams
Anytime you apply concepts
to different situations
7/42
Knowing how to break a problem down into steps
is the key to solving any kind of problem!
General Problem
Solving Strategy
8/42

5-Step Problem Solving Strategy
Identify what is being given1
General steps for solving any type of problem in
physics:
Identify what is being given.
Clarify what is being asked.
Select a strategy
1
2
3
If unclear, try to rephrase it.
Trial & error, search, deductive reasoning, working
backwards or knowledge-based.
9/42
Solve using the selected strategy
Review
4
5
backwards or knowledge based.
Check for reasonableness, units and significant figures.
Applying the “General” Strategy
This general strategy will work for any type of
problem in physics, not just “math” problems.y j
Calculations, concepts, diagrams, etc.
10/42

Problem Solving Example #1
Step
Id tif h t’ i 10201
Description Information
Example: How many significant digits are in 1020 g?
Identify what’s given
Identify what’s being asked
Strategy: Knowledge based
Apply strategy: Count the
1020 g
? Significant digits
Use your knowledge of significant digits to
count.
There is no decimal point—count digits
between the first and last non-zero number.
1
2
3
4 1020 g 3 significant digits
11/42
significant digits4
Review5
1020 g 3 significant digits
The rule without a decimal place is count
between the non-zero numbers. There are 3
“102” significant figures.
Problem Solving Example #2
Step
Identify what’s given Force & acceleration1
Description Information
Example: What is the relationship between force and
acceleration?
Identify what s given
Identify what’s being
asked
Strategy: Deductive
reasoning
Force & acceleration
What is the relationship? Is it direct (as one
increases, the other does also) or indirect (as
one increases, the other decreases)
Force is the push on an object
Acceleration is the rate of change of velocity
Look for any mathematical equations
Force = m * a
1
2
3
12/42
Apply the strategy:
Deduce the relationship4
Review5
If force increases, the “push” increases.
Therefore the acceleration will increase.
The harder you push on an object, the greater
the change of velocity

Word Problem
Solving Strategy
13/42
Word Problem Woes
Many people are intimidated by word
problems…they don’t know where to
begin.
Instead of seeing them as word
problems, use the KUDOS method to
14/42
turn them into simple calculation
problems.

The KUDOS Method
Known
Unknown
Definition
O t t
15/42
Output
Substantiation
Step “K”
Identify what is known.K
“Known”
Tip Example
A car travels 15.2 m
A car travels 15.2 m
“m” (meters) is a
distance unit. The
statement is giving
distance (“d”)
d = 15.2 m
Use units to identify
information
Write information
symbolically
16/42
A book is accelerating
across a table
Therefore there
is a net force
Look for implied
information

Step “U”
Identify what is unknownU
“Unknown”
Tip Example
How many Newtons…
How many Newtons…
Newtons is a
force unit
F = ? N
What is the problem
looking for?
Write information
symbolically
17/42
This helps you focus on the “goal”
Step “D”
Define needed informationD
“Definition”
Tip Example
Velocity needs to be
converted to m/s
Solve for distance
knowing velocity and
time
1 km/h = 0.27 m/s
Find equalities to
convert
Choose & re-
arrange equations t
d
V = So tVd ×=
18/42
There’s a constant in the
equation, such as “g”
You’re missing a piece of
information and cannot
find it elsewhere
Look on a cheat-
sheet of constants
Look for another
equation or
approach
Look other places
for missing info
Re-evaluate your
approach if
needed

Step “O”
Find the output of your informationO
“Output”
dtV =×
gmW ×=
“g” is acceleration due
to gravity
Tip Example
12.5m/s × 1.25s = d
Plug values into
equations
Use fundamental
constants if
needed
19/42
12.5m/s × 1.25s = d
12.5m/s × 1.25s = d 15.6 m =d
needed
Check unit
cancellation
Perform the
calculation
12.5m/s × 1.25s = d
Step “S”
Substantiate your results with a 1-2-3 check:S
“Substantiation”
Are the units remaining after
cancellation appropriate?
Are the results reasonable
& possible?
When solving for mass,
you should get a mass
unit
Tip Example
Is it 10,000 when it
should be 10?
1. Check Validity
2. Check Units
20/42
× or ÷ use least # of s.f
in problem
+ or - use least # of
decimal places in
problem
Are the significant figures in
the answer correct?
3. Check
Significant
Figures

Connecting the Known and Unknown
One of the hardest things for students is determining
how to get from the known to the unknown…
?Known UnknownDefinition
21/42
The “Definitions” (Step “D”) shows the connections!
Using Symbols Effectively
Physics uses so many symbols that are similar that
it can quickly become confusing.
Try to label symbols with something meaningful andy y g g
mnemonic to help you sort them out.
To symbolize this… Don’t use
this…
m1 & m2
Instead use
this…
mp & mn
Mass of proton & mass of
neutron
22/42
p1 & p2
V1 & V2
pl & pq
Vc & Vt
Momentum of linebacker and
momentum of quarterback
Velocity of car & velocity of
truck

KUDOS Example #1
Example:
Step Source Information Write down
What is the net force if a girl pulls with 27 N and
a boy pulls with 14 N in the other direction?
Force of girl
What is the net force?
Net force is the sum of all forces
Fg= 27 N
Given forces in “N”
Fnet = ? N
Fnet = Fg + Fb
K
U
D
Force of boy Fb = -14 N (opposite direction, so “-”)
Fnet = Fg + Fb
23/42
O
validity, units & significant figures
13N is a reasonable answer
“N” is a force unit
0 decimal places given 0 in
answer
S
Calculate Fnet
g
Fnet = (27 N) + (-14 N)
Fnet = 13N
KUDOS Example #2
Example: Find the focal length of a mirror if a 2.0 cm tall object is 5.0 cm
from the mirror appears with a 4.0 cm tall image.
Step Source Information Write down
2.0 cm tall object
What is the focal length
Equation to find focal length
ho = 2.0 cm
f = ? cm
K
U
D
Object is 5.0 cm from the lens do = 5.0 cm
Distances of image and object are related to
heights
do
1
di
1
1
f
+
=
do
di
ho
hi −
=
4.0 cm tall image hi = 4.0 cm
But “di” is not known
di
ho
hi
do =×−
24/42
O
validity, units & sig figs
10 cm is a reasonable answer
“cm” is the unit used for other
lengths
2 s.f. given 2 s.f. in answer
S
Calculate di and then calculate f
g
10cmdi
2.0cm
4.0cm
5.0cm −==×−
10cm
5.0cm
1
10cm
1
1
f =
+
−
=

KUDOS Example #3
Example:
Step
30.0 V
V = 30 0 V
Source Information Write down
Find current in a circuit with a 30.0 V battery and a 10.0Ω
resistor.
“V” is a voltage unit
Find current (which is measured in Amps)
V 30.0 V
I = ? A
K
U
D
10.0Ω
“Ω” is a resistance unit
R = 10.0 Ω
Define resistance & solve for current
I
V
R = So
R
V
I =
R
V
I =
25/42
O
validity, units & sig figs
3.0 A is reasonable for current
“A” is a valid unit for current
3 s.f. given 3 s.f. in answer
S
Solve for current
R
I = 30.0 V / 10.0 Ω
I = 3.00 A
Connecting the “General” Strategy & KUDOS
Problem Solving
5-Step General
problem-solving
strategy
For any type of problem, use
26/42
KUDOS
method
For word problems, the 5-step
process becomes

Physics
Exams
27/42
Help for Physics Exams
So now that you know how to
attack individual problems using
th P bl S l i St tthe Problem-Solving Strategy, or
the KUDOS method for word
problems…
How do you attack the big
problem…the exam?
28/42

Types of Exams
Short answer exams Assessing
First, understand the two types of exams:
Short answer exams – Assessing
knowledge of physics facts.
Long answer exams Assessing
Fill in the blank, True/False, Multiple-choice,
matching
29/42
Long answer exams – Assessing
critical thinking, application of
concepts, problem-solving.
Essay, calculation problems
Exam-Prep Tips
Stay ahead of the game1
Here are some helpful hints for preparation
Begin preparing early…the night before should be for
Make a cheat sheet2
Even if you can’t use it on the test, creating a cheat-
sheet is an excellent way to review the important
information.
brief overview after studying for several night, not
cramming as your only preparation!
30/42
Know the format & what information is “test-able”3
Focus your energy…know what you will tested on and
how they will test it.

Exam-Prep Tips (Con’t)
Make a mock-exam4
Try choosing the 5 most important topics and writing
Attend the review session5
Even if this session is optional, GO! Instructors often
give extra help and hints of what will be on the exam at
these sessions.
questions about them.
31/42
Get help early6
Don’t wait until the last minute to ask questions…do so
well in advance (at least 2 days before the exam so that
you have time to apply the information and make sure you
understand it).
Exam Taking Tips
Arrive early and prepared1
Here are some helpful hints for taking your exam
Rushing or searching for supplies builds anxiety
Listen & read instructions carefully2
Don’t assume you know the instructions…read them
carefully.
If the instructor gives any last-minute changes or
instructions, be sure to pay attention and write them
down!
32/42
Memory dump first3
down!
Write down any equations or facts that you’ve been
remembering on the top or back of the test first thing.
Once you have them to refer to, you’ll be calmer taking
the test. Do this on the test, not scratch paper to avoid
accusations of cheating!

Exam Taking Tips (Con’t)
Skim the test and make a plan4
Budget your time according to length and difficulty of
Answer questions sequentially5
Often the answer to or information from a previously
problem is re-used.
questions.
33/42
Apply the guessing rule6
Don’t just randomly guess. Use your information and
understanding to eliminate wrong answers. Eliminate as
many as you can and then guess from the remaining if
you’re not sure.
Multiple-Choice Tip #1
Scan all the choices1
Here are some helpful hints for multiple-choice exams
Often one choice looks good…but a later one isg
better. Look at them all before choosing.
Which of the following would cause the largest
error in a lab determining force by measuring
mass & acceleration?
A. Misreading the balance
B. Misreading the stopwatch
Example:
34/42
B. Misreading the stopwatch
C. Only performing one trial
While A & B would cause errors, C would cause the
largest error.

Avoid the word trap2
There’s often more than one way to say something…the test
may use another word than the one you’re used to, but they
may mean the same thing
Multiple-Choice Tip #2
may mean the same thing.
Thermal energy flows from an object with ____
kinetic energy to an object with ____ kinetic
energy?
A. More, less
B. Less, more
C. High, the same
Example:
35/42
D. Thermal energy does not flow from one object
to another
“Thermal energy” = heat
“Kinetic energy” = energy of motion
Rephrase using more familiar terms:
Essay Tip #1
Understand the question1
Here are some helpful hints for essay exams
Be familiar with questions that include:q
Describe: Give a detailed & sequential account of facts
Discuss: Give a detailed analysis of all facts from your
point of view
Calculate: Use givens & constants to find a numerical
answer
36/42
Evaluate: Give a judgment given a set of facts
Explain: Give a rationale for a set of facts—don’t just
rephrase the facts!
Compare/contrast: Give similarities (compare) and
differences (contrast)

Just answer the question2
Be sure that you’ve covered everything asked
Essay Tip #2
Be sure that you ve covered everything asked
for…but that’s it. Don’t spend time including extra
information (that may not be correct and count
against you!)
Describe how mass relates to acceleration with a net force.Example:
37/42
Don’t discuss everything you know about mass,
acceleration and net force…just answer the question
asked.
Watch your time3
Don’t get stuck on one
Essay Tip #3
Don t get stuck on one
question—divide your
time according to length
of exam and difficulty of
questions.
38/42

Free-Response Tips
Show partial work!1
Here are some helpful hints for free-response exams
Show as much work as possible so the instructor
Don’t forget the unit!2
This is an easy point to miss…make sure every
answer has a unit!
Show as much work as possible so the instructor
can see your thought process. Many give partial
credit if they can see what you understood and
where your mistake was
39/42
Don’t judge length of answer on blank space3
answer has a unit!
Tests often have too much or too little blank space
after a question…don’t think a question with a lot of
blank space requires a long answer and vice versa.
Be sure to
thoroughly
Be sure to
thoroughly
A problem:
anytime you
don’t know how
A problem:
anytime you
don’t know how
Do your best
on exams by
f ll i
Do your best
on exams by
f ll i
Learning Summary
thoroughly
prepare for
the exam.
thoroughly
prepare for
the exam.
to get from
where you are
to where you
need to be.
to get from
where you are
to where you
need to be.
following
exam-taking
tips!
following
exam-taking
tips!
U blU bl
40/42
Use the KUDOS
problem solving
technique for word
problems.
Use the KUDOS
problem solving
technique for word
problems.
Use problem-
solving
techniques for
every type of
problem.
Use problem-
solving
techniques for
every type of
problem.

Congratulations
You have successfully completed
the tutorial
Problem Solving in
PhysicsPhysics
Wh t’ N t
Chemistry :: Biology :: Physics :: Math
What’s Next …
Step 1: Concepts – Core Tutorial (Just Completed)
Step 2: Practice – Interactive Problem Drill
Step 3: Recap – Super Review Cheat Sheet
42/42
Go for it!
http://www.RapidLearningCenter.com

problem_solving in physics

More Related Content

What's hot (17)

Viewers also liked (14)

Similar to problem_solving in physics (20)

More from Timothy Welsh (20)

Recently uploaded (20)

problem_solving in physics