A charged particle is projected with velocity v0 along positive x-axis. The magnetic field B is directed along negative z-axis between x = 0 and x = L. The particle emerges out (at x = L) at an angle of 60º with the direction of projection. Find the velocity with which the same particle  were projected (at x = 0) along positive x-axis so that when it emerges out (at x = L), the angle made by it is 30º with the direction of projection