2026 F = ma Exam — Question 16 — Physics Guide

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F = ma (11–17)

Momentum

FMA-2026-16 · 2026 F = ma (AAPT)

2026 F = ma Exam — Question 16

A small puck of mass m slides without friction inside a rigid, uniform triangle rack of mass 5m, whose inner boundary is an equilateral triangle ABC. The rack is initially at rest and can move freely on a frictionless horizontal table. All collisions between the puck and the rack are perfectly elastic. At some instant, the puck strikes the midpoint of side AB from inside the rack. Just before this collision, the puck’s velocity is parallel to side BC. After the collision at the midpoint of AB, the puck collides with the rack again, and then collides once more. At which part of the triangle does this second collision after the initial one occur? (Some answer choices refer to the midpoint D of side AC.) C D ⃗v A B — Source: Question 16, 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.