Chapter 4 - Kinematics in Two Dimensions - Exercises and Problems - Page 106: 9

$a = (2~\hat{i}-8~\hat{j})~m/s^2$

$v(t) = (2t~\hat{i}+(3-t^2)~\hat{j})~m/s$ $a(t) = \frac{dv}{dt}$ $a(t) = (2~\hat{i}-2t~\hat{j})~m/s^2$ At t = 4 s: $a = (2~\hat{i}-(2)(4)~\hat{j})~m/s^2$ $a = (2~\hat{i}-8~\hat{j})~m/s^2$