Answer
$v = -(1.50~m/s)\hat{j}$
Work Step by Step
We can find the time when $v_x = 0$:
$v_{xf} = v_{i0}+a_x~t$
$t = \frac{v_{xf} - v_{i0}}{a_x}$
$t = \frac{0 - 3.00~m/s}{-1.00~m/s^2}$
$t = 3.00~s$
We can find $v_y$ at $t = 3.00~s$:
$v_{yf} = v_{y0}+a_y~t$
$v_{yf} = 0+(-0.500~m/s^2)(3.00~s)$
$v_{yf} = -1.50~m/s$
We can write the velocity vector in unit-vector notation:
$v = -(1.50~m/s)\hat{j}$
