일반물리학 1 — Motion in Two and Three Dimensions: Problem 6

6 An electron’s position is given by $\vec{r} = 3.00t\hat{i} - 4.00t^2\hat{j} + 2.00\hat{k}$, with $t$ in seconds and $\vec{r}$ in meters. (a) In unit-vector notation, what is the electron’s velocity $\vec{v}(t)$? At $t = 3.00\text{ s}$, what is $\vec{v}$ (b) in unit-vector notation and as (c) a magnitude and (d) an angle relative to the positive direction of the $x$ axis?