A $0\mathrm{.}5$ kg block B slides without Fiction inside a slot cut in arm OA$.$ which rotates in vertical plane $($Fig $).$ The motion of the rod is defined by the relation theta dot$=10$rads$^(2),$constant. At this instant when theta $=45$degree,r$=0\mathrm{.}8$ m and the velocity of the block is zero at this instant:

a$)$ Draw the EBD on the block and determine the force exerted on the block by the arm.

b$)$ Determine the relative acceleration of the block with respect to the arm