How to Review for the AP Physics Exam

Solving physics problems is like mastering any sport or musical instrument: If you want to do it well, you have to practice. Do not expect to understand everything immediately, and do not be frustrated by the effort required to master some concepts and techniques. Contrary to popular conceptions of a vast divide between physics geniuses who can immediately solve problems and other people who simply cannot, learning physics requires hard work. However, a mastery of calculus-based physics will teach you analytical and mathematical skills that will prove extremely useful in a broad range of other disciplines.

Guide to This Review Book

Text

The text of the chapters works from the ground up without assuming extensive knowledge of physics on your part. Therefore, the text is appropriate at any stage of your mastery of AP Physics. You may find it helpful to read the text along with your textbook when you are first learning the material and studying for course exams, or you may choose to read the chapters together as a review after you have completed most of your AP Physics course.

Questions

Because of space limitations, it is impossible for the questions to work from the ground up (i.e., start with very easy questions and progress to more difficult ones). Therefore, the questions are generally near the AP level and assume that you have some problem-solving experience. The questions are designed to raise you from a competent problem solver to an expert with extensive experience in solving AP problems. If you have difficulty with the questions, you may want to go back and solve some problems in your introductory physics textbook or AP Physics textbook, as well as consider the advice in the next paragraph.

Difficulty of the Questions

The problems in this review book are generally slightly more difficult than actual AP exam questions. In order to maximize the amount that you learn from this book and your degree of comfort with AP Physics questions, we have designed the questions to cover the material and problem-solving techniques of the AP Physics exam while being more challenging than questions you are actually likely to encounter on the exam. For example, our problems generally have more parts than standard AP problems in order to exhaustively explore various hypothetical situations. Therefore, we strongly urge you not to become discouraged if you are not able to solve all the problems on your first attempt. Instead, the best approach is to make your best effort at the problems, read (and study) the solutions of problems you got wrong, and later return to these problems and try them again. Because we have attempted to include all the common problem types that appear on the AP exam, after you have worked through all the problems in this guide correctly (even if not on your first or second attempt), you will probably be in excellent shape. Another approach that you might find useful for multistep problems is to do each part individually and check the answer before proceeding to the next part. This allows you to avoid wasting time by making a mistake in one part and then propagating it through the rest of the problem.

The advantage to this difficulty level is that after you obtain experience solving the problems in this book, you will be comfortable solving the problems on the AP exam.

Distribution of the Questions

Not all AP topics are created equal. Some topics (such as Gauss’s and Faraday’s laws) are tested extensively and are frequently the subject of entire free-response questions. Other topics (such as circuit analysis) are central to solving a range of questions but are generally not the sole topic of a free-response question. Finally, some topics (such as Maxwell’s equations) are not tested very extensively.

The distribution of questions in this review book is based on a careful review of decades of AP examinations. Topics that have been tested frequently in the past are reviewed thoroughly, and topics tested infrequently are not reviewed as extensively. Additionally, more attention is paid to topics requiring more practice than others. (For example, although rotational kinematics is frequently tested, extensive practice with rotational kinematics is not crucial because of its similarity to linear kinematics.) We appreciate that the time you have to review for this exam is limited, so we have worked hard to provide you with exactly the material and questions you need to do well on the AP exam.

Derivations

From introductory physics courses, you may have received the impression that derivations aren’t very important but rather that only the final results are relevant. This is not the case in Physics C, where the level of sophistication is high enough to require the derivation of most of the important equations. Since these derivations illustrate important principles and problem-solving approaches, we have included them here and urge you to make sure you understand them.

Problem-Solving Strategies to Watch For

As multiple-choice and free-response questions are presented and explained, we have tried to show, often in multiple approaches to the same problem, how various strategies can be applied. A quick way to answer a multiple-choice question, for example, often involves elimination of incorrect choices based on such considerations as dimensional analysis, behavior at extreme values of the system parameters, results of eliminating certain parameters, and the absence of parameters that by the nature of the problem must be included. In the free-response questions, results from previous parts frequently are used in later, more involved, parts; thus, notice how you can get valuable clues as to how to approach part (d) by rereading (and probably using results from) parts (a), (b), and (c). Remember the value of getting a good grasp of the situation described in a problem; using sketches, diagrams, and graphs; thinking of the relationships between given quantities; and relating situations to concepts that might be more familiar (as in rotational and linear motion, in electrical and gravitational fields, and in conservation of elastic and gravitational energy). As you carefully study our solutions, be sure to watch for these and the many other approaches that will improve your abilities to analyze and to understand physics problems and to develop your “physics intuition.”

Graphical Analysis of Data

The free-response section of the exam typically includes a question involving a lab experiment and data analysis. We have included such questions in this edition. Here are some general tips for successfully solving these questions.

■You will usually be asked to plot a relationship between quantities that is expected to be linear. You may need to evaluate a suitable function of one of the quantities in order to obtain a linear relation. For an example, see “Mechanics III” of the diagnostic test (page 18).

■If you are asked to plot quantity A as a function of quantity B, then A is on the vertical axis and B is on the horizontal axis. On the other hand, the problem may simply say to plot the data to test a linear relationship. In that case, it is your choice as to which quantity goes on which axis.

■You will need to examine the range of data points to determine the correct scale on the axes. Your data points should cover at least half of the grid. Your scale must be uniform along the axis; i.e., if neighboring major gridlines differ by 4 units, then this must be true of all neighboring major gridlines.

■Label the axes with the quantity plotted, and be sure to include the units.

■If you are asked to fit the data to a linear relationship, draw a straight line that best follows the trend of the data. Your line need not (and, in general, won’t be able to) pass through all of the data points. Do not draw a jagged line that connects neighboring points! Your goal is to draw a single straight line that best approximates the data.