Multivariable Calculus, 7th Edition

Published by Brooks Cole
ISBN 10: 0-53849-787-4
ISBN 13: 978-0-53849-787-9

Chapter 16 - Vector Calculus - 16.7 Exercises - Page 1145: 15

Answer

$\dfrac{\pi(391\sqrt{17}+1)}{60}$

Work Step by Step

The flux through a surface can be defined only when the surface is orientable. We know that $\iint_S F \cdot dS=\iint_S F \cdot n dS$ Here, $n$ denotes the unit vector. Since, $\iint_S y dS =\iint_{R} y \sqrt {1+4z^2+4x^2} dA$ $=\int_{0}^{2\pi} \int_0^2 r^3 \sqrt {1+4r^2} dr d\theta$ Plug $a=1+4r^2 \implies da=8r dr$ $=\dfrac{1}{8} \int_{0}^{2 \pi} \int_1^{17} a^{1/2} \times \dfrac{a-1}{4} du d \theta$ $=\dfrac{1}{32} \int_{0}^{2 \pi}(2/5) a^{5/2} -(2/3) a^{3/2}|_1^{17} d\theta$ $=\dfrac{1}{32} \int_{0}^{2 \pi} \dfrac{1564 \sqrt{17}+4}{15} d\theta$ $=\dfrac{\pi(391\sqrt{17}+1)}{60}$
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