PHYC 162 Homework #1
Due in recitation Friday, January 21
Typical homework assignments in this class will consist of conceptual questions, textbook
problems, a context-rich problem, and a meta-homework question. I will also be giving
you a weekly problem solving tip, which you should read.
Conceptual Questions
Each chapter of the textbook contains “Conceptual Questions” and “Exercises and
Problems”. For example, chapter 14’s Conceptual Questions are on p. 435 and the
Problems start on p. 436. Be sure you check the type of question when you complete your
homework.
The Questions check conceptual understanding without requiring any calculations. Your
answer should include 1-3 sentences of explanation; single word answers will not be
accepted. You may include diagrams if you find it helpful.
1. Chapter 14 Conceptual Question 1
2. Chapter 14 Conceptual Question 2
3. Chapter 14 Conceptual Question 3
4. Chapter 14 Conceptual Question 7
5. Chapter 14 Conceptual Question 9
Exercises and Problems
Problems will be graded based on a logical and complete problem solving strategy, as
outlined in the weekly problem solving tips and the 5 step problem strategy demonstrated
in lecture. SHOW YOUR WORK, including diagrams, algebraic equations, and enough
written explanations that somebody who is not familiar with the problem could
understand what you are doing. Note that a final numerical answer is only one small part
of a complete solution; an answer with no work shown will not be given any credit.
1. Chapter 14 Exercise 12
2. Chapter 14 Exercise 21
3. Chapter 14 Problem 51
4. Chapter 14 Problem 68
5. Chapter 14 Problem 77
Context-rich Problem
This last problem is known as a context-rich problem. Typical textbook problems save
you, the student, a lot of work by explicitly giving all necessary information, not giving
irrelevant information, providing diagrams, and asking questions with easily identifiable
goals. Unfortunately, gathering relevant information, drawing applicable diagrams, and
asking good questions are very important skills that are required everywhere outside the
classroom. Context-rich problems are designed to help you practice these skills.
A child’s slingshot uses a stretched rubber band, which can be approximated as an ideal
spring, to shoot a glass marble. You see the child pull back his slingshot by 25 cm, taking
aim at a car’s windshield, so you take away the slingshot. You wonder if the marble
would be moving fast enough to break the windshield. You estimate that if the marble is
moving at higher than 30 mph, it has a good chance of breaking the windshield. You tape
the marble to the rubber band for safety. When you let go, the marble, still attached to the
rubber band, oscillates with a period of 0.11 s. Can the slingshot shoot the marble fast
enough to break the car’s windshield?
Meta-homework
The document on the following page includes a problem solving tip for this week. These
tips will train you in the nuts and bolts of problem solving. The meta-homework questions
will help you practice these specific skills. You should read the problem solving tip before
you answer the meta-homework question. Answers should be written in a few sentences
unless other specific directions are given.
There are a few traits and attitudes that are essential to being a good problem solver:
confidence, concentration, determination, and creativity. Arming yourself with
confidence and determination and practicing concentration and creativity can help you
immensely. When you begin a problem, how confident are you that you will be able to
figure out a way to solve it? Are you determined enough to try several approaches to a
problem before you solve it or give up? How long are you able to concentrate on a
problem? Does your work environment allow you to concentrate? Are you creative
enough to try an approach to a problem without knowing it will work, or do you always
try to follow a pattern you have seen before?
Example: I am always very confident that I can eventually find a solution to a problem. If
I am having difficulty, the problem becomes a death match for me. I am willing to focus
on a problem for several hours or even days if necessary. In fact, I make sure that I have
at least an hour of uninterrupted time in a quiet area with nothing but music before I try to
solve a problem. Usually when I am solving a real problem, as opposed to an exercise
which I already know how to do, I find that a creative approach is necessary. I usually
have to try 2 or 3 approaches before I find one that works.
Peanut’s Problem Solving Tips – Week 1
“A good physicist writes like a journalist, works like a clerk, and thinks like a poet.”
-Richard Feynman
Introduction
It is my intent throughout the semester to provide you with some practical
suggestions to help you develop habits for working and thinking that will aid you not
only in this course, but also in other scientific and engineering pursuits. Similar
approaches can also prove useful in nearly anything you do, from changing the oil in your
car to writing papers for a literature class.
This series of problem solving tips will begin with a very broad look at the way
physicists think about problems, then progressively dig deeper into the details of specific
tricks and tools that are helpful. Some of these tips will come naturally to some of you; if
this is the case I am very pleased, yet I still encourage you pay attention because being
aware of the intricacies of your thought processes will help you avoid mental blocks and
will greatly enhance your ability to communicate your thoughts to others. Other tips will
deal with things you already know, like algebra, in an organized manner that will
streamline the problem solving process. A few tips may introduce you to entirely new
tricks that can get you out of trouble spots.
Much of the mechanics of what I will present to you will require some discipline
and a little extra effort on your part. For example, I find that students are reluctant to take
the time to draw good diagrams and solve equations algebraically instead of numerically.
I was at one time just as stubborn as any of you in this; my high school physics teacher
spent two frustrating years (frustrating for both of us) trying to get me to work with
discipline. As one who has been through this fight, I urge you to determine from the
beginning to try to “work like a clerk” even though it may be aggravating at times. In just
a few weeks you will get the hang of it and you will save yourself a lot of trouble in the
long run. I suggest that you practice using the techniques I will describe when you do the
homework problems. The homework sets in this class will include “meta-homework”
questions specifically designed to help you practice the week’s problem solving tip.
The 5 Step Strategy
I will begin with an outline of the entire process that a physicist goes through
when solving problems. This will follow the discussion presented in “The Competent
Problem Solver for Introductory Physics” by Ken Heller. This treatment was created
based on detailed interviews of professional physicists. I can attest that this is the way
that physicists typically approach problems.
The basic structure can be broken down into 5 steps, each essential. The steps are:
1. Focus the problem – Understand what is going on in the problem. Usually, this
requires a visual picture and drawing diagrams is often appropriate. Determining
from the problem statement what is known and what you need to find should also
be done in this step.
2. Describe the physics – This is in my opinion the key step to the entire process.
Here you describe qualitatively what is happening and determine what law or
laws of physics apply to the situation.
3. Plan the solution – Write down equations that describe the laws of physics that
you have decided to use. Check that you have enough information to solve these
equations for what you need to find.
4. Execute the plan – This is the mechanical step that will hopefully become
automatic for you. Mathematical techniques are used to solve your equations here.
5. Evaluate the answer – Plug in numbers if appropriate. Check that your numbers
are reasonable in magnitude and units. Check that you have answered the right
question.
There you have the basics. I will go into each of these steps in more detail in the
coming weeks with examples. Start practicing.