AP Physics 1 Free Response Question for Kinematics

👋 Welcome to the AP Physics Unit 1 FRQ (Kinematics) 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.)

Learning Objectives & Science Practices

• 3.A.1.1 Express the motion of an object using narrative, mathematical, and graphical representations. [SP 1.5, 2.1, 2.2]
• 4.A.2.1 Make predictions about the motion of a system based on the fact that acceleration is equal to the change in velocity per unit time, and velocity is equal to the change in position per unit time. [SP 6.4]
• 4.A.2.3 Create mathematical models and analyze graphical relationships for acceleration, velocity, and position of the center of mass of a system and use them to calculate properties of the motion of the center of mass of a system. [SP 1.4, 2.2]

Reference Video

https://www.youtube.com/watch?v=fhOqbAF1Uis

Setup

A student of mass m stands on a platform scale in an elevator in a tall building. The positive direction for all vector quantities is upward. The vertical position of an elevator as a function of time is shown below. The velocity at 6 seconds is -30 m/s.

Questions with Answers & Rubric

(a) On the grid below, plot the velocity of the elevator as a function of time. (3pts)

• 1pt: For a horizontal line at 20 m/s from t=0 to t=2

• 1pt: For a straight line starting at 20 m/s at t=2, and ending at 0 m/s at t=4

• 1pt: For a straight line starting at 0 m/s at t=4, and ending at -30 m/s at t=6 📄 Additional Resources

• Replay: Velocity vs. Time Graphs

(b) Calculate the average acceleration for the time period t = 2s to t = 4s. (3pts)

• 1pt: For a description or equation for acceleration either as the slope of the v vs. t graph, or a = ∆v / ∆t

• 1pt: For the work to determine the acceleration, a = (0-20) / (4-2)

• 1pt: For the correct answer with units, a = -10 m/s^2 📄 Additional Resources

• Study Guide: Position, Velocity, and Acceleration

An inspector provides the student with the following graph showing the acceleration a of the elevator as a function of time t.

(c) During what time interval(s) is the speed of the elevator constant? How do you know? (3pts)

• 1pt: For the time interval of 10-13 sec
• 1pt: For the time interval of 19-20 sec
• 1pt: For a correct explanation that for a constant velocity, the acceleration of the system must be equal to 0

📄 Additional Resources

• Replay: Acceleration

Next Steps

• 🧠 Want to continue reinforcing your knowledge of Unit 1? Check out Unit 1 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 2 resources.
• • 📚 Want to review multiple units? Check out all of the AP Physics FRQs.