Period $(T)=2 \,s$

$\omega=\frac{2 \pi}{2}=\pi \,rad / s$

When block just represent from a piston, maximum acceleration must be equal to $g$.

$g=-\omega^2 x$

Acceleration is maximum when $x=A$

$g=-\omega^2 A$

or $A=\frac{9.8}{\pi^2}$

Maximum velocity $=A \omega$

$=\frac{9.8}{\pi^2} \times \pi$

$=\frac{9.8}{\pi} \,m / s$

$=3.119 \,m / s =3.12 \,m / s$