2009 F = ma Exam — Question 25 — Physics Guide

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FMA-2009-25 · 2009 F = ma (AAPT)

2009 F = ma Exam — Question 25

25. Two discs are mounted on thin, lightweight rods oriented through their centers and normal to the discs. These axles are constrained to be vertical at all times, and the discs can pivot frictionlessly on the rods. The discs have identical thickness and are made of the same material, but have diﬀering radii r1 and r2. The discs are given angular velocities of magnitudes ω1 and ω2, respectively, and brought into contact at their edges. After the discs interact via friction it is found that both discs come exactly to a halt. Which of the following must hold? Ignore eﬀects associated with the vertical rods. r1 r2 — Source: Question 25, 2009 F = ma Exam, © 2009 American Association of Physics Teachers (AAPT) and the U.S. Physics Team. Adapted by PhysicsTrainer: reformatted into a separate question and answer choices for online multiple-choice practice; any shared setup from nearby questions is repeated here. Not affiliated with or endorsed by AAPT or the U.S. Physics Team.

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F = ma problems are © the American Association of Physics Teachers (AAPT) and the U.S. Physics Team, the original source, and are used with permission. Problems shown here are adaptations: they have been reformatted by Physics Guide into separate question and answer-choice pieces for online multiple-choice practice. Physics Guide is an independent student project and is not affiliated with, endorsed by, operated by, or supported by AAPT, F = ma, USAPhO, or the U.S. Physics Team.

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