Calculus: Early Transcendentals 8th Edition

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

Chapter 13 - Review - Exercises - Page 882: 17

Answer

Velocity: $$ \begin{aligned} \mathbf{v}(t) &=\left\langle 1+\ln t, 1, -e^{-t} \right\rangle \end{aligned} $$ Acceleration: $$ \begin{aligned} \mathbf{a}(t)&=\left\langle \frac{1}{t}, 0, e^{-t} \right\rangle \end{aligned} $$ Speed: $$ \begin{aligned} |\mathbf{v}(t)| =\sqrt{2+2 \ln t+(\ln t)^{2}+e^{-2 t}}. \end{aligned} $$

Work Step by Step

We have the position function: $$ \begin{aligned} \mathbf{r}(t)&=t \ln t \mathbf{i}+t \mathbf{j}+e^{-t} \mathbf{k} \\ &=\left\langle t \ln t, t, e^{-t} \right\rangle \end{aligned} $$ The velocity is found by deriving the position: $$ \begin{aligned} \mathbf{v}(t) &=\mathbf{r}^{\prime}(t)\\ &=(1+\ln t) \mathbf{i}+\mathbf{j}-e^{-t} \mathbf{k}\\ &=\left\langle 1+\ln t, 1, -e^{-t} \right\rangle \end{aligned} $$ The acceleration is found by deriving the velocity: $$ \begin{aligned} \mathbf{a}(t)&=\mathbf{v}^{\prime}(t)\\ &=\frac{1}{t} \mathbf{i}+e^{-t} \mathbf{k}\\ &=\left\langle \frac{1}{t}, 0, e^{-t} \right\rangle \end{aligned} $$ The speed is the scalar version of velocity: $$ \begin{aligned} |\mathbf{v}(t)| &=\sqrt{(1+\ln t)^{2}+1^{2}+\left(-e^{-t}\right)^{2}} \\ &=\sqrt{2+2 \ln t+(\ln t)^{2}+e^{-2 t}}. \end{aligned} $$
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