The potential energy of a $1 \mathrm{~kg}$ particle free to move along the $x$-axis is given by $V(x)=\left(\frac{x^{4}}{4}-\frac{x^{2}}{2}\right) \mathrm{J}$. The total mechanical energy of the particle is $2 \mathrm{~J}$. Then, the maximum speed (in $\mathrm{m} / \mathrm{s}$ ) is [2006]
(A) $\frac{3}{\sqrt{2}}$
(B) $\sqrt{2}$
(C) $\frac{1}{\sqrt{2}}$
(D) 2