Answer
$v_0 = 6.4~m/s$
Work Step by Step
We can use conservation of energy to solve this question:
$KE_0 = KE_f + PE_f$
$\frac{1}{2}mv_0^2 = \frac{1}{2}mv_f^2 + mgy$
$v_0^2 = v_f^2 + 2gy$
$v_0 = \sqrt{v_f^2 + 2gy}$
$v_0 = \sqrt{(0.50 ~m/s)^2 + (2)(9.80 ~m/s^2)(2.10 ~m)}$
$v_0 = 6.4~m/s$