College Physics (4th Edition)

Published by McGraw-Hill Education
ISBN 10: 0073512141
ISBN 13: 978-0-07351-214-3

Chapter 2 - Multiple-Choice Questions - Page 63: 11


(c) The two coins start to slide at the same time

Work Step by Step

The correct answer is: (c) The two coins start to slide at the same time Let $\mu_s$ be the coefficient of static friction. Let $m$ be the mass of an object on the book cover. For any angle $\theta$, the maximum possible force of static friction is $mg~cos(\theta)~\mu_s$. The force directed down the slope is $mg~sin(\theta)$. We can find the angle when the object starts to slide: $mg~sin(\theta) = mg~cos(\theta)~\mu_s$ $tan(\theta) = \mu_s$ $\theta = arctan(\mu_s)$ The angle $\theta$ does not depend on the mass. Therefore, the two coins would start to slide at the same time.
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