Calculus (3rd Edition)

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

Chapter 17 - Line and Surface Integrals - 17.2 Line Integrals - Exercises - Page 732: 25

Answer

$\mathop \smallint \limits_C^{} {\bf{F}}\cdot{\rm{d}}{\bf{r}} = \frac{{10}}{9}$

Work Step by Step

We have the vector field ${\bf{F}}\left( {x,y,z} \right) = \left( {\frac{1}{{{y^3} + 1}},\frac{1}{{z + 1}},1} \right)$ and the parametrization ${\bf{r}}\left( t \right) = \left( {{t^3},2,{t^2}} \right)$ for $0 \le t \le 1$. So, we obtain ${\bf{F}}\left( {{\bf{r}}\left( t \right)} \right) = \left( {\frac{1}{9},\frac{1}{{{t^2} + 1}},1} \right)$ $d{\bf{r}} = {\bf{r}}'\left( t \right)dt$ $d{\bf{r}} = \left( {3{t^2},0,2t} \right)dt$ Evaluate the dot product ${\bf{F}}\left( {{\bf{r}}\left( t \right)} \right)\cdot{\bf{r}}'\left( t \right)dt$: ${\bf{F}}\left( {{\bf{r}}\left( t \right)} \right)\cdot{\bf{r}}'\left( t \right)dt = \left( {\frac{1}{9},\frac{1}{{{t^2} + 1}},1} \right)\cdot\left( {3{t^2},0,2t} \right)dt$ $ = \left( {\frac{1}{3}{t^2} + 2t} \right)dt$ Evaluate $\mathop \smallint \limits_C^{} {\bf{F}}\cdot{\rm{d}}{\bf{r}}$ using Eq. (8): $\mathop \smallint \limits_C^{} {\bf{F}}\cdot{\rm{d}}{\bf{r}} = \mathop \smallint \limits_a^b {\bf{F}}\left( {{\bf{r}}\left( t \right)} \right)\cdot{\bf{r}}'\left( t \right){\rm{d}}t$ $\mathop \smallint \limits_C^{} {\bf{F}}\cdot{\rm{d}}{\bf{r}} = \mathop \smallint \limits_0^1 \left( {\frac{1}{3}{t^2} + 2t} \right){\rm{d}}t$ $ = \left( {\left( {\frac{1}{9}{t^3} + {t^2}} \right)|_0^1} \right) = \frac{1}{9} + 1 = \frac{{10}}{9}$ So, $\mathop \smallint \limits_C^{} {\bf{F}}\cdot{\rm{d}}{\bf{r}} = \frac{{10}}{9}$.
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