Answer
$v = 0.56 \,\text{m/s}$
Work Step by Step
From the conservation law of energy, we get the velocity as next
$$U + K = 0=\frac{1}{2} k y^{2}-m g y+\frac{1}{2} m v^{2}$$
Solve for $v$ we get it by
\begin{align*}
v&=\sqrt{2 g y-\frac{k}{m} y^{2}} \\
&= \sqrt{2 g y-\frac{g}{l} y^{2}}\\
&= \sqrt{2\left(9.8 \mathrm{m} / \mathrm{s}^{2}\right)(0.08 \mathrm{m})-\left(\frac{9.8 \mathrm{m} / \mathrm{s}^{2}}{0.05 \mathrm{m}}\right)(0.08 \mathrm{m})^{2}}\\
&= 0.56 \,\text{m/s}
\end{align*}
