---
title: "Flywheels (rapidly rotating disks) are widely used in industry for storing energy. They are spun up slowly when extra energy is available, then decelerate quickly when needed to supply a boost of energy. A flywheel, \\( 20 \\text{ cm} \\) in diameter, can spin at \\( 20{,}000 \\text{ rpm} \\)."
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url: "https://nerd-notes.com/ubq/39133/"
date_modified: "2025-12-14T03:38:05+00:00"
---

# Flywheels (rapidly rotating disks) are widely used in industry for storing energy. They are spun up slowly when extra energy is available, then decelerate quickly when needed to supply a boost of energy. A flywheel, \( 20 \text{ cm} \) in diameter, can spin at \( 20{,}000 \text{ rpm} \).

Flywheels (rapidly rotating disks) are widely used in industry for storing energy. They are spun up slowly when extra energy is available, then decelerate quickly when needed to supply a boost of energy. A flywheel, \( 20 \text{ cm} \) in diameter, can spin at \( 20{,}000 \text{ rpm} \).

**Part a)** What is the speed of a point on the rim of this flywheel? *(3 points)*

**Part b)** Suppose the flywheel’s angular velocity decreases by \( 40\)% over \( 30 \, \text{s}\) as it supplies energy. What is the magnitude of the rotor’s angular acceleration? Assume that the angular acceleration is constant. *(3 points)*

**Part c)** How many revolutions does the rotor make during these \( 30 \, \text{s}\)? *(3 points)*


*The answer key and step-by-step explanation are available to logged-in users at https://nerd-notes.com/ubq/39133/*