Answer
(a) $v_{f}=27.9~m/s$ due north
(b) $v_{f}=9.48~m/s$ due north
Work Step by Step
Let the positive direction be the north. South is the negative direction. So. $v_{i}=+18.1~m/s$.
$a_{av}=\frac{\Delta v}{\Delta t}$. Now, rearrange the equation:
$\Delta v=(a_{av})(\Delta t)=a\times\Delta t$
(a) $a=1.30~m/s^{2}$ and $\Delta t=7.50~s$
$\Delta v=v_{f}-v_{i}$
$v_{f}=v_{i}+\Delta v=v_{i}+a\times \Delta t=18.1~m/s+(1.30~m/s^{2})(7.50~s)=27.9~m/s$
(b) $a=-1.15~m/s^{2}$ and $\Delta t=7.50~s$
$\Delta v=v_{f}-v_{i}$
$v_{f}=v_{i}+a\times\Delta t=18.1~m/s+(-1.15~m/s^{2})(7.50~s)=9.48~m/s$
