Calculus: Early Transcendentals 8th Edition

Published by Cengage Learning
ISBN 10: 1285741552
ISBN 13: 978-1-28574-155-0

Chapter 16 - Section 16.9 - The Divergence Theorem - 16.9 Exercise - Page 1146: 14

Answer

$4 \pi R^5$

Work Step by Step

The Divergence Theorem states that $\iint_S \overrightarrow{F}\cdot d\overrightarrow{S}=\iiint_Ediv \overrightarrow{F}dV $ Here, $S$ is a closed surface and $E$ is the region inside that surface. $div F=\dfrac{\partial a}{\partial x}+\dfrac{\partial b}{\partial y}+\dfrac{\partial c}{\partial z}$ This implies that $div F=(x^2+y^2+z^2) \cdot \lt x,y,z \gt=3(x^2+y^2+z^2)+2(x^2+y^2+z^2)=5(x^2+y^2+z^2)=5\rho^2 $ Now, we have $Flux=\int_{0}^{2 \pi}\int_0^{\pi} \int_{0}^{R} 5\rho^2 dv$ $=\int_{0}^{2 \pi}\int_0^{\pi} \int_{0}^{R} 5\rho^2 \sin \phi d \rho d\phi d \theta$ $=\int_{0}^{2 \pi}\int_0^{\pi} \int_{0}^{R} 5\rho^2 \sin \phi d \rho d\phi d \theta$ $=\int_{0}^{2 \pi}\int_0^{\pi} R^5 \sin \phi d \rho d\phi d \theta$ $=\int_{0}^{2 \pi} R^5 [(-\cos \phi)_0^{\pi} d \theta$ $=\int_{0}^{2 \pi} 2 R^5 d \theta$ $=4 \pi R^5$
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