Answer
$\vec{u}=-5\vec{j}$
Work Step by Step
$\vec{u}=\langle0,-5\rangle$
To represent this vector in terms of $\vec{i}$ and $\vec{j}$, just write the first component of $\vec{u}$ times $\vec{i}$ plus the second component of $\vec{u}$ times $\vec{j}$:
$\vec{u}=\langle0,-5\rangle=0\vec{i}-5\vec{j}=-5\vec{j}$
