Chapter 11 - Vectors and Vector-Valued Functions - 11.7 Motion in Space - 11.7 Exercises - Page 826: 9

a) $\textbf{v}(t) = <2, -4>$; Speed = $2\sqrt {5}$ b) $\textbf{a}(t) = <0, 0>$

$\textbf{r}(t) = <2 + 2t, 1-4t>$ $\textbf{v}(t) = \textbf{r}'(t) = <2, -4>$ Speed = $|\textbf{v}(t)| = \sqrt {(2)^2+(-4)^2} = 2\sqrt {5}$ $\textbf{a}(t) = \textbf{v}'(t) = <0, 0>$