It is not a question of asymptotic complexity as an algorithm cannot perform negative work. It is a question about growth of functions.
We know as n gets higher Ω($n^{2}$) approaches + infinity , whereas (5-$n^{3}$) approaches - infinity.
This can be visualized on a cartesian plane. Hence the given expression is false because Ω($n^{2}$) will always be greater than (5-$n^{3}$) for higher values of n.