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 $=A \omega$
$=\frac{9.8}{\pi^2} \times \pi$
$=\frac{9.8}{\pi} \,m / s$
$=3.119 \,m / s =3.12 \,m / s$



$(A)$ the speed of the particle when it returns to its equilibrium position is $u_0$.
$(B)$ the time at which the particle passes through the equilibrium position for the first time is $t=\pi \sqrt{\frac{ m }{ k }}$.
$(C)$ the time at which the maximum compression of the spring occurs is $t =\frac{4 \pi}{3} \sqrt{\frac{ m }{ k }}$.
$(D)$ the time at which the particle passes througout the equilibrium position for the second time is $t=\frac{5 \pi}{3} \sqrt{\frac{ m }{ k }}$.