2025 F = ma Exam — Question 7 — Physics Guide

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FMA-2025-07 · 2025 F = ma (AAPT)

2025 F = ma Exam — Question 7

A mechanism consists of three point masses, each of mass m, connected by two massless rods of length l and a torsion spring acting as a hinge. The potential energy of the torsion spring is given by Us . This system is designed to “walk” down a set of stairs, as shown in the figure. The angles θ1 and θ2 (see figure) represent the orientation of the rods, and their rates of change, ω1 and ω2 , are the corresponding angular velocities. Assume that the mass on the surface is instantaneously at rest. Which equation correctly describes the total energy of the system? m m m θ2 θ1 — Source: Question 7, 2025 F = ma Exam, © 2025 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.

AP Physics 1 and AP Physics C (Mech) problems are adapted from OpenStax College Physics for AP® Courses 2e and University Physics Volume 1, © OpenStax (Rice University), licensed under CC BY 4.0. Problem text is reproduced exactly; correct answers come from the OpenStax answer keys. For written-answer problems, the incorrect answer choices were written by Physics Guide. Physics Guide is not affiliated with or endorsed by OpenStax or the College Board.