A small, 0.6-lb collar D can slide on portion AB of a rod which is bent as shown. Knowing that r = 8 in and that the rod rotates about the vertical AC at a constant rate of 10 rad/s, determine the smallest allowable value of the coefficient of static friction between the collar and the rod if the collar is not to slide when a) a =15° b)a = 45°. Indicate for each case the direction of the impending motion.