Unit 3 FRQ (Circular Motion & Gravitation) Answers

AP Physics 1 Free Response Question Answers for Circular Motion & Gravitation

Setup

Questions with Answers & Rubric

Part A

(i) Without manipulating equations, state whether the rider feels lighter, heavier, or the same as they normally would while standing still on earth. Briefly explain your reasoning. (2pts)

• 1pt: The rider feels lighter.
• 1pt: The normal force of the rider is smaller than the force due to gravity, since the rider is going over the hill and the net force is directed in the direction of the center of the circle (down, in this case).

• Study Guide: Applications of Newton’s Second Law

(ii) On the dot below, draw and label a free body diagram for the rider at point a. (2pts)

• Study Guide: Free-Body Diagrams for Objects in Uniform Circular Motion

(iii) How heavy would a 60 kg passenger feel at point a? (What is their apparent weight?) Make sure you show ALL work! (3pts)

• 1pt: Fn = 503.2 N

• Study Guide: Applications of Newton's Second Law

Part B

(i) Without manipulating equations, state whether the rider is moving faster, slower, or the same speed at point b as they were at point a. Briefly explain your reasoning. (2pts)

• 1pt: The rider is moving faster.
• 1pt: The rider has potential energy due to gravity at point a, which is then converted to kinetic energy at point b, and therefore must have more speed at b.

• Study Guide: Conservation of Energy, the Work-Energy Principle, and Power

(ii) On the dot below, draw a free body diagram for the rider. (2pts)

• Study Guide: Free-Body Diagrams for Objects in Uniform Circular Motion

(iii) How fast is the rider traveling at point b? Make sure to show all your work. (4pts)

• 1pt: V = 19.7 m/s

• Study Guide: Centripetal Acceleration and Centripetal Force

Part C

(i) On the dot below, draw a free-body diagram for the rider at point c. (2pts)

(ii) Determine the radius of the track at point c. Make sure to show all work. (2pts)

• 1pt: r = 2.94m

Next Steps

• 🧠 Want to continue reinforcing your knowledge of Unit 3? Check out Unit 3 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 4 Resources.
• 📚 Want to review multiple units? Check out all of the AP Physics 1 FRQs.
• 🤝 Got more questions? Want to help others studying the same topic? Jump into a room in Hours!