\(\mathrm{mg}-\mathrm{N}=\mathrm{m} \omega^{2} \mathrm{x}\)
where \(x\) is the distance from mean position
For block to leave contact \(\mathrm{N}=0\)
\(\Rightarrow m g=m \omega^{2} x \Rightarrow x=\frac{g}{\omega^{2}}\)
$\left(g=10 \,{m} / {s}^{2}\right)$