Its a Physics Question I am stuck with.?

A disk s placed on a inclined plane with angle of inclination 'theta'. The disk is given an initial velocity of v(o) at an angle 'phi(o)'=90deg. where phi is the angle between the direction of motion of the disk and the x axis in the plane of the incline. The coefficient of friction is mu=tan(theta). The m of the disk is m. Calculate the relation between the velocity v of the disk and the angle 'phi'.