2026 F = ma Exam — Question 20 — Physics Guide

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FMA-2026-20 · 2026 F = ma (AAPT)

2026 F = ma Exam — Question 20

Two uniform rigid rods lie in a vertical plane. The lower rod rests on a rough horizontal table at a single point O and makes angle θ ̸= 0 with the vertical. The rod can pivot about point O without slipping. The second rod is rigidly attached at its center of mass to the top of the lower rod at point P . A motor causes the second rod to rotate in the plane about P . The motor is rigidly attached to the lower rod and does not exert forces or torques on the table. P θ O g table Which of the following types of motion of the second rod could keep the angle θ fixed in time? — Source: Question 20, 2026 F = ma Exam, © 2026 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.