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Unit 5 FRQ (Momentum) Answers

3 min readβ’november 29, 2021

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AP Physics 1 Free Response Question Answers for Momentum

π Welcome to the AP Physics Unit 5 FRQ (Momentum) Answers. Have your responses handy as you go through the rubrics to see how you did!
β± 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

Identical blocks 1 and 2 are placed on a horizontal surface at points A and E, respectively, as shown. The surface is frictionless except for the region between points B and C, where the surface is rough. Beginning at time tA, Block 1 is pushed with a constant horizontal force from Point A to Point B by a mechanical plunger.
Upon reaching Point B, Block 1 loses contact with the plunger and continues moving to the right along the horizontal surface toward Block 2. Block 1 collides with and sticks to Block 2 at Point E, after which the two-block system continues moving across the surface, eventually passing Point F.

Part A

(i) On the axes below, sketch the speed of the center of mass of the two-block system as a function of time, from time tA until the blocks pass Point F at time tF. The times at which Block 1 reaches Points A through F are indicated on the time axis. (3pts)

Part B

The system is reset and Block 1 is again released. The following conditions now exist:
 Mass of Block 1 (kg) Mass of Block 2 (kg) Spring Constant (N/m) Distance Between Each Letter Coefficient of Friction, Β΅ 5 3 825 1.2 0.15
In addition, there is no friction on the horizontal surface except for between letters B and C.

(i) Determine the speed of Block 1 at Point B. (3pts)

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(ii) Determine the speed of Block 1 at Point D. (4pts)

(iii) Determine the speed of the combined Blocks 1 and 2 at Point F. (2pts)

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Part C

(i) Was momentum and/or energy conserved from Point D to Point F? Briefly explain your reasoning for EACH. (2pts)

 Conserved Not Conserved Momentum x Energy x
• 1pt: Momentum is conserved in a closed system for a perfectly inelastic collision.
• 1pt: Energy is NOT conserved in a perfectly inelastic collision.
NOTE: Points may be earned for correct explanations, even if the wrong boxes are checked.
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Next Steps

• π§  Want to continue reinforcing your knowledge of Unit 5? Check out Unit 5 Trivia, either as a document or as a game.
• β­ Ready to move on to the next topic? Take a look at the collection of Unit 6 Resources.
• π Want to review multiple units? Check out all of the AP Physics 1 FRQs.
• π€ Got more questions? Want to help others studying the same topic? Jump into a room in Hours!
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πUnit 1 β Kinematics
πUnit 2 β Dynamics
πUnit 3 β Circular Motion & Gravitation
β‘οΈUnit 4 β Energy
β³οΈUnit 5 β Momentum
πΈUnit 6 β Simple Harmonic Motion
π‘Unit 7 β Torque & Rotational Motion
π‘Unit 8 β Electric Charges & Electric Force
πUnit 9 β DC Circuits
πUnit 10 β Mechanical Waves & Sound
πAP Physics Essentials
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