How to Approach the Multiple-Choice Section for AP Physics B & C
You cannot use a calculator on the multiple-choice section of the AP exam. "No calculator!" you exclaim. "That's inhumane!" Truth be told, you are not alone in your misguided fears. Most students are totally distraught over not being able to use their calculators. They think it's entirely unfair.
But the fact is: the AP test is very, very fair. There are no trick questions on the AP exam, no unreasonably difficult problems, and no super-tough math. So when the test says, "You may not use a calculator on this section," what it really means is, "You DON'T NEED to use a calculator on this section." In other words, the writers of the test are trying to communicate two very important messages to you. First, no question on the multiple-choice section requires lots of number crunching. Second,
Yes, you must use numbers occasionally. Yet you must understand that the number you get in answer to a question is always subordinate to what that number represents.
Many misconceptions about physics start in math class. There, your teacher shows you how to do a type of problem, then you do several variations of that same problem for homework. The answer to one of these problems might be 30,000,000, another 16.5. It doesn't matter … in fact, the book (or your teacher) probably made up random numbers to go into the problem to begin with. The "problem" consists of manipulating these random numbers a certain way to get a certain answer.
In physics, though, every number has meaning. Your answer will not be 30,000,000; the answer may be 30,000,000 electron-volts, or 30,000,000 seconds, but not just 30,000,000. If you don't see the difference, you're missing the fundamental point of physics.
We use numbers to represent REAL goings on in nature. 30,000,000 eV (or, 30 MeV) is an energy; this could represent the energy of a particle in a multibillion dollar accelerator, but it's much too small to be the energy of a ball dropped off of a building. 30,000,000 seconds is a time; not a few hours or a few centuries, but about one year. These two "30,000,000" responses mean entirely different things. If you simply give a number as an answer, you're doing a math problem. It is only when you can explain the meaning of any result that you may truly claim to understand physics.
So How Do I Deal with all the Numbers on the Test?
You see, the test authors aren't dumb—they are completely aware that you have no calculator. Thus, a large majority of the multiple-choice questions involve no numbers at all! And those questions that do use numbers will never expect more than the simplest manipulations. Here is a question you will never see on the AP test:
Yes, we know you might have seen this type of problem in class. But it will not be on the AP exam. Why not? Plugging numbers into a calculator is not a skill being tested by this examination. (You should have recognized that the equation necessary to solve this problem is though.) We hope you see that, without a calculator, it is pointless to try to get a precise numerical answer to this kind of question.