Unit 2 FRQ (Dynamics) Answers

AP Physics 1 Free Response Question Answers for Dynamics

👋 Welcome to the AP Physics Unit 2 FRQ (Dynamics) Answers. Have your responses handy as you go through the rubrics to see how you did!

⏱ Remember, the AP Physics 1 exam has 5 free-response questions, and you will be given 90 minutes to complete the FRQ section. (This means you should give yourself ~18 minutes to go through each practice FRQ.)

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Setup

A worker pushes a wooden crate up a ramp at a constant velocity. The ramp has been covered with a material that when warm provides enough friction that it will not slide down the hill. When the ramp is exposed to the cold the coefficient of friction changes enough that the box will easily slide down the ramp.

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Questions with Answers & Rubric

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(a) Draw a free body diagram for the box on the top dot and a free body diagram with components on the bottom dot. The dotted line represents the incline. (3pts)

📄 Additional Resources

• Replay: Free-Body Diagrams

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(b) In the space provided below, derive an equation for the coefficient of friction, 𝜇, when the box is moving up the hill at constant velocity. Express your answer in terms of m, g, Fapp, trig identities, and 𝜃.

📄 Additional Resources 

• Study Guide: Contact Forces

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(c) If the mass of the box is 25 kg, the applied force is 250 N, and the angle 𝜃 is 22o, calculate the coefficient of friction using your equation from part b) as the person is pushing the box up the hill. Show all work. (1pt)

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(d) The ramp is now chilled until the coefficient of friction equals 0.02 and the box begins to accelerate down the incline. In addition, the person is no longer pushing the box. In the space provided below, draw a free body diagram for the box on the top dot and a free body diagram with components on the bottom dot. The dotted line represents the incline. (3pts)

📄 Additional Resources 

• Replay: Typical Dynamics Problems

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(e) Derive an equation for the acceleration of the box as it slides down the hill. Express your answer in terms of m, g, 𝜇, trig identities, and 𝜃. (4pts)

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(f) Calculate the acceleration of the box down the hill using the information given in parts (a) through (e). Show all work. (2pts)

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Next Steps

• 🧠 Want to continue reinforcing your knowledge of Unit 2? Check out Unit 2 Trivia, either as a document or as a game.
• • ⏭ Ready to move on to the next topic? Take a look at the collection of Unit 3 Resources.
• • 📚 Want to review multiple units? Check out all of the AP Physics 1 FRQs.

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