The equation of projectile is  $Y=\sqrt{3}X-\frac{1}{2}g{X}^2$ The  velocity of projection is

Comparing with  $y=x\tan \theta -\frac{g{x}^2}{2u^2{\cos }^2\theta }$ we have

$\tan \theta =\sqrt{3}\text{ or }\theta =60°\text{ and }{u}^2{\cos }^2\theta =1$

or           $u=\sec \theta =\sec 60°=2{ \mathrm{ms}}^{-1}$