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Free Response Questions (FRQs)

Unit 3 FRQ (Circular Motion & Gravitation) Answers

3 min readβ€’november 29, 2021


AP Physics 1 🎑

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

πŸ‘‹ Welcome to theΒ AP Physics Unit 3 FRQ (Circular Motion & Gravitation) Answers.Β 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.)

Setup

https://firebasestorage.googleapis.com/v0/b/fiveable-92889.appspot.com/o/images%2F-46ZNQeZ7UkKq.png?alt=media&token=07d4f418-f4be-4ec6-b45f-38bd0aab37e3
A portion of a rollercoaster is shown above. At point a, the track has a radius of approximately 3.0 m and the cart has a speed of 2.2 m/s. The mass of the rider is approximately 60 kg. We will be ignoring the mass of the car.

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

https://firebasestorage.googleapis.com/v0/b/fiveable-92889.appspot.com/o/images%2F-oJg4VE2DkTaN.png?alt=media&token=9772a671-534d-4385-b874-5855cf8bc770
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(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
https://firebasestorage.googleapis.com/v0/b/fiveable-92889.appspot.com/o/images%2F-qLMI0ugqRrCu.png?alt=media&token=c837aa2f-1b21-420f-b0ef-cd63a763a638
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Part B

At point b, the track has a radius of 13m and the rider feels four times heavier than normal.Β 

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

https://firebasestorage.googleapis.com/v0/b/fiveable-92889.appspot.com/o/images%2F-2kfKLpHTgLLs.png?alt=media&token=5eaca200-a157-40a9-a020-a6f8cb410b4f
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(iii) How fast is the rider traveling at point b? Make sure to show all your work. (4pts)

  • 1pt: V = 19.7 m/s
https://firebasestorage.googleapis.com/v0/b/fiveable-92889.appspot.com/o/images%2F-RGGpiJM2E7Om.png?alt=media&token=cfe10385-7b16-459b-aaaf-63f6745c2740
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Part C

At point c, the track and cart exert a force of 400 N on the 60 kg rider. Their velocity is 7.0 m/s.

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

https://firebasestorage.googleapis.com/v0/b/fiveable-92889.appspot.com/o/images%2F-dUvLu1TW2wom.png?alt=media&token=09fbe6e8-e20c-4702-9e65-1a4d1be18dda

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

  • 1pt: r = 2.94m
https://firebasestorage.googleapis.com/v0/b/fiveable-92889.appspot.com/o/images%2F-J7RjSWxaM9sx.png?alt=media&token=9a5f3860-fa36-41d7-a908-9f38415a60cf

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.
  • πŸ“š 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!

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