Physics for Scientists and Engineers: A Strategic Approach with Modern Physics (3rd Edition)

Published by Pearson
ISBN 10: 0321740904
ISBN 13: 978-0-32174-090-8

Chapter 12 - Rotation of a Rigid Body - Exercises and Problems - Page 350: 40

Answer

$ 2\;\hat i-6\;\hat j-9\;\hat k$

Work Step by Step

We need to find $\vec A\times \vec B$ where $$\vec A=3\;\hat i+1\;\hat j+0\;\hat k$$ and $$\vec B=3\;\hat i-2\;\hat j+2\;\hat k$$ Thus, $$\vec A\times \vec B=(3\;\hat i+1\;\hat j+0\;\hat k)\times (3\;\hat i-2\;\hat j+2\;\hat k)$$ $$\vec A\times \vec B=(3\;\hat i\times3\;\hat i )+(3\;\hat i\times-2\;\hat j )+(3\;\hat i\times2\;\hat k)\\ +(1\;\hat j\times3\;\hat i )+(1\;\hat j\times-2\;\hat j )+(1\;\hat j\times2\;\hat k)\\ +(0\;\hat k\times3\;\hat i )+(0\;\hat k\times-2\;\hat j )+(0\;\hat k\times2\;\hat k)$$ Recall that $\hat i\times \hat i=\hat j\times \hat j=\hat k\times \hat k=0$; So, $$\vec A\times \vec B=0+\overbrace{(3\;\hat i\times-2\;\hat j )}^{-6\;\hat k}+\overbrace{(3\;\hat i\times2\;\hat k)}^{-6\;\hat j}\\ +\overbrace{(1\;\hat j\times3\;\hat i )}^{-3\;\hat k}+0+\overbrace{(1\;\hat j\times2\;\hat k)}^{2\;\hat i}\\ +0+0+0$$ $$\boxed{\vec A\times \vec B= 2\;\hat i-6\;\hat j-9\;\hat k}$$
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