A mass is attached to one end of a massless string(length $l$) the other end of which is attached to a fixed support O. The mass swings around in a vertical circle as shown in figure. The mass has the minimum speed $(u=\sqrt{5gl})$ necessary at the lowermost point of the circle to keep the string from going slack  ($g=10m/s^2$ ) 

If you cut the string when it is making angle $\theta$ (as shown in the figure) with upper vertical line through centre O of the circle, the resulting projectile motion of the mass has its maximum height located directly above the center of the circle? Find the value of  $10\cos \theta$