일반물리학 1 — Motion in Two and Three Dimensions: Problem 16

16 The velocity $\vec{v}$ of a particle moving in the $xy$ plane is given by $\vec{v} = (6.0t - 4.0t^2)\hat{i} + 8.0\hat{j}$, with $\vec{v}$ in meters per second and $t (> 0)$ in seconds. (a) What is the acceleration when $t = 2.5\text{ s}$? (b) When (if ever) is the acceleration zero? (c) When (if ever) is the velocity zero? (d) When (if ever) does the speed equal $10\text{ m/s}$?