Work, Energy and Power: JEE Main 2006 Physics question

The potential energy of a $1$ $kg$ particle free to move along the $x$-axis is given by $V\left( x \right) = \left( {{{{x^4}} \over 4} - {{{x^2}} \over 2}} \right)J$. The total mechanical energy of the particle is $2J.$ Then, the maximum speed (in $m/s$) is