Lab Questions for AP Physics B & C

It is all well and good to be able to solve problems and calculate quantities using the principles and equations you've learned. However, the true test of any physics theory is whether or not it WORKS.

The AP development committee is sending a message to students that laboratory work is an important aspect of physics. To truly understand physics, you must be able to design and analyze experiments. Thus, each free-response section will contain at least one question that involves experiment design and analysis.

Here's an example:

To answer a lab question, just follow these steps:

1. Follow the directions.

Sounds simple, doesn't it? When the test says, "Draw a diagram," it means they want you to draw a diagram. And when it says, "Label your diagram," it means they want you to label your diagram. You will likely earn points just for these simple steps.



2. Use as few words as possible.

Answer the question, then stop. You can lose credit for an incorrect statement, even if the other 15 statements in your answer are correct. The best idea is to keep it simple.

3. There is no single correct answer.

Most of the lab questions are open-ended. There might be four or more different correct approaches. So don't try to "give them the answer they're looking for." Just do something that seems to make sense—you might well be right!

4. Don't assume you have to use all the stuff they give you.

It might sound fun to use a force probe while determining the index of refraction of a glass block, but, really! A force probe!?!

5. Don't over-think the question.

They're normally not too complicated. Remember, you're supposed to take only 10–15 minutes to write your answer. You're not exactly designing a subatomic particle accelerator.

6. Don't state the obvious.

You may assume that basic lab protocols will be followed. So there's no need to tell the reader that you recorded your data carefully, nor do you need to remind the reader to wear safety goggles.

Now Put It All Together

Here are two possible answers to the sample question. Look how explicit we were about what quantities are measured, how each quantity is measured, and how μ_k is determined. We aren't artistes, so our diagram doesn't look so good. But for the AP exam, we believe in substance over style. All the necessary components are there, and that's all that matters.

Answer #1

In the laboratory, you are given a metal block, about the size of a brick. You are also given a 2.0-m-long wooden plank with a pulley attached to one end. Your goal is to determine experimentally the coefficient of kinetic friction, μ_k, between the metal block and the wooden plank.

1. From the list below, select the additional equipment you will need to do your experiment by checking the line to the left of each item. Indicate if you intend to use more than one of an item.



2. Draw a labeled diagram showing how the plank, the metal block, and the additional equipment you selected will be used to measure μ_k.
3. Briefly outline the procedure you will use, being explicit about what measurements you need to make and how these measurements will be used to determine μ_k.

Use the balance to determine the mass, m, of the metal block. The weight of the block is mg. Attach the spring scale to the bulldozer; attach the other end of the spring scale to the metal block with string. Allow the bulldozer to pull the block at constant speed.

The block is in equilibrium. So, the reading of the spring scale while the block is moving is the friction force on the block; the normal force on the block is equal to its weight. The coefficient of kinetic friction is equal to the spring scale reading divided by the block's weight.