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# How to Approach the Free-Response Section for AP Physics B & C (page 3)

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By McGraw-Hill Professional
Updated on Feb 14, 2011

### Math and the Physics C Exam

Physics C students often worry about the math they're expected to know for the AP exam, because some of the material covered in the Physics C curriculum involves pretty complicated calculus. Maxwell's equations, for example, involve concepts that are well beyond the scope of most high school calculus classes.

But even though some fancy math shows up in the Physics C curriculum, the math on the AP exam is generally less daunting. Of the 45 points available on each free-response section, it's very rare when more than three or four of these points are awarded for evaluating an integral or derivative. So if you're not a calculus fan, it's okay to pledge to evaluate no integrals on the free-response section, and you can still get a 5 just fine!

The way you succeed without doing much calculus is to have a strong understanding of the physical meaning behind the mathematics. The problems that might seem to involve calculus—those that use an integral or derivative equation from the equations sheet—can usually be approached with algebraic methods. Remember, an integral is just the area under a graph; a derivative is just the slope of a graph. If you have to, set up an integral and don't solve it. Or explain in words what your answer should look like. Also, note that many of the equations that appear on the equations sheet as calculus expressions rarely or never need calculus. For instance, Gauss's law has a nasty integral in it, but when used correctly, Gauss's law rarely requires any calculus. Whatever you do, it is not worth the time and frustration to worry too much about the tough calculus—this isn't a math exam, and the point distribution in the rubrics reflects this fact.

• Always show your work. If you use the correct equation to solve a problem but you plug in the wrong numbers, you will probably get partial credit, but if you just write down an incorrect answer, you will definitely get no partial credit.
• If you don't know precisely how to solve a problem, simply explain your thinking process to the grader. If a problem asks you to find the centripetal acceleration of a satellite orbiting a planet, for example, and you don't know what equations to use, you might write something like this: "The centripetal force points toward the center of the satellite's orbit, and this force is due to gravity. If I knew the centripetal force, I could then calculate the centripetal acceleration using Newton's second law." This answer might earn you several points, even though you didn't do a single calculation.
• Let's say that part (b) of a question requires you to use a value calculated in part (a). You didn't know how to solve part (a), but you know how to solve part (b). What should you do? We can suggest two options. First, make up a reasonable answer for part (a), and then use that answer for part (b). Or, set some variable equal to the answer from part (a) (write a note saying something like, "Let v be the velocity found in part (a)"). Then, solve part (b) in terms of that variable. Both of these methods should allow you to get partial or even full credit on part (b).
• If you make a mistake, cross it out. If your work is messy, circle your answer so that it's easy to find. Basically, make sure the AP graders know what you want them to grade and what you want them to ignore.
• If you're stuck on a free-response question, try another one. Question #6 might be easier for you than question #1. Get the easy points first, and then only try to get the harder points if you have time left over.
• Always remember to use units where appropriate.
• 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 15–17 minutes to solve. They're not designed to be outrageously difficult, so if your answer to a free-response problem is outrageously complicated, you should look for a new way to solve the problem, or just skip it and move on.

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