Answer
$v=-7i+7\sqrt3j.$
Work Step by Step
If a vector $v=ai+bj$ makes an angle of $\alpha$ with the positive x-axis and has magnitude $||v||=\sqrt{a^2+b^2}$, then $a=||v||cos\alpha$ and $v=||v||sin\alpha$.
Hence here $a=||14||cos(120^\circ)=-7$ and $v=||14||sin(120^\circ)=7\sqrt3$. Therefore $v=-7i+7\sqrt3j.$
