# How Do I Calculate Net Force on Charges in AP Physics B 2005 Form B Question 3?

• mitiejoe
So, in summary, Joe is struggling with Question 3 of the 2005 AP Physics B Free-Response Questions from Form B. He is unsure if he is on the right track and is seeking clarification on how to find the net force on the -Q charge in part a. The net force is in the positive x direction and the y forces cancel.
mitiejoe
I have been working on the 2005 AP Physics B Free-Response Questions from Form B. Question 3 is giving me a lot of difficulty, and I am not sure if i am going in the right direction. The question can be found here:

For part a, the force on the -Q charge is (2KQ^2)/5a^2, from each of the -2Q charges. To find the net force, do I have break that into X and Y components and add them together as vectors?

-joe

Yes, the net force is in the positive x direction, the y forces cancel.

Hello Joe,

I'm glad to hear that you are working on the 2005 AP Physics B Free-Response Questions from Form B. Question 3 can definitely be tricky, so it's great that you are seeking clarification.

For part a, you are correct in your calculation of the force on the -Q charge. This force comes from the electric field created by the two -2Q charges, and can be found using Coulomb's Law.

To find the net force, you will indeed need to break the force into its X and Y components and then add them together as vectors. This is because the two -2Q charges are not aligned with the -Q charge, so their forces will have both X and Y components. You can use trigonometry to find the components of each force, and then add them together to find the net force.

Remember to pay attention to the directions of the forces and their components when adding them together. This will ensure that your final answer is accurate.

I hope this helps and good luck with the rest of the questions!

## 1. What topics were covered in the 2005 AP Physics B Form B exam?

The 2005 AP Physics B Form B exam covered topics such as kinematics, dynamics, energy, momentum, circular motion, gravitation, simple harmonic motion, electricity, magnetism, and optics.

## 2. How many multiple-choice questions were on the 2005 AP Physics B Form B exam?

There were 70 multiple-choice questions on the 2005 AP Physics B Form B exam.

## 3. What types of free-response questions were asked on the 2005 AP Physics B Form B exam?

The free-response section of the 2005 AP Physics B Form B exam consisted of five questions, including two experimental design questions, one short-answer question, and two long-answer questions.

## 4. How long was the 2005 AP Physics B Form B exam?

The 2005 AP Physics B Form B exam was 3 hours long, with 90 minutes for the multiple-choice section and 90 minutes for the free-response section.

## 5. What score was needed to pass the 2005 AP Physics B Form B exam?

The passing score for the 2005 AP Physics B Form B exam was a 3, with scores ranging from 1 to 5. However, the actual score needed to pass may vary depending on the college or university's credit policies.

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