Calculus (3rd Edition)

Published by W. H. Freeman
ISBN 10: 1464125260
ISBN 13: 978-1-46412-526-3

Chapter 9 - Further Applications of the Integral and Taylor Polynomials - 9.3 Center of Mass - Exercises - Page 483: 18

Answer

$$\left( \frac{6}{15},\frac{1}{2}\right)$$ $$M_x=\frac{1}{15},\ \ \ \ \ M_y=\frac{1}{12} $$

Work Step by Step

given $$ y=x,\ \ \ \ \ \ y=x^2 ,\ \ \ \ \ 0\leq x\leq 1 $$ Since $$ x\geq x^2 \ \ \ \text{for }\ 0\leq x\leq 1 $$ Then \begin{align*} M_x&=\frac{1}{2}\int_{0}^{1}[f(x)]^2-[g(x)]^2dx\\ &= \frac{1}{2}\int_{0}^{1}[ x^2-x^4] dx\\ &= \frac{1}{2}[\frac{1}{3}x^3-\frac{1}{5}x^5]\bigg|_{0}^{1}\\ &= \frac{1}{15} \end{align*} and \begin{align*} M_y&= \int_{0}^{1}x[[f(x)] -[g(x)] ]dx\\ &= \int_{0}^{1}[ x^2-x^3] dx\\ &= [\frac{1}{3}x^3-\frac{1}{4}x^4]\bigg|_{0}^{1}\\ &= \frac{1}{12} \end{align*} and \begin{align*} M &= \int_{0}^{1} [[f(x)] -[g(x)] ]dx\\ &= \int_{0}^{1}[ x -x^2] dx\\ &= [\frac{1}{2}x^2-\frac{1}{3}x^3]\bigg|_{0}^{1}\\ &= \frac{1}{6} \end{align*} Hence \begin{align*} \left( \bar{x},\bar{y}\right)&=\left(\frac{M_{x}}{M}, \frac{M_{y}}{M}\right)\\ &=\left( \frac{6}{15},\frac{1}{2}\right) \end{align*}
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