---
title: "A student is initially at rest on a stool that is free to rotate without friction about a vertical axis. The student holds a bicycle wheel that is spinning such that its angular momentum vector \\(\\vec{L}_w\\) points vertically upward. The student then flips the wheel over so that its angular momentum vector points vertically downward. Which of the following correctly describes the motion of the student-stool system after the flip and provides a valid justification?"
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url: "https://nerd-notes.com/ubq/109822/"
date_modified: "2026-03-26T05:52:35+00:00"
---

# A student is initially at rest on a stool that is free to rotate without friction about a vertical axis. The student holds a bicycle wheel that is spinning such that its angular momentum vector \(\vec{L}_w\) points vertically upward. The student then flips the wheel over so that its angular momentum vector points vertically downward. Which of the following correctly describes the motion of the student-stool system after the flip and provides a valid justification?

A student is initially at rest on a stool that is free to rotate without friction about a vertical axis. The student holds a bicycle wheel that is spinning such that its angular momentum vector \(\vec{L}_w\) points vertically upward. The student then flips the wheel over so that its angular momentum vector points vertically downward. Which of the following correctly describes the motion of the student-stool system after the flip and provides a valid justification?

- **A.** The student-stool system rotates such that its angular momentum is vertically upward because the total angular momentum of the student-stool-wheel system must be conserved.
- **B.** The student-stool system rotates such that its angular momentum is vertically downward because the torque exerted by the student on the wheel results in an equal and opposite torque on the student.
- **C.** The student-stool system rotates such that its angular momentum is vertically upward because the rotational kinetic energy of the system must be conserved during the flip.
- **D.** The student-stool system does not rotate because the internal torque exerted by the student on the wheel is canceled by the internal torque exerted by the wheel on the student.

*The answer key and step-by-step explanation are available to logged-in users at https://nerd-notes.com/ubq/109822/*