A thin, uniform, metal bar, 3 meter long and weighing 90 Newton, is hanging vertically from the ceiling by a frictionless pivot. Suddenly it is struck 1.5 meter below the ceiling by a small 2 kilogram ball, initially traveling horizontally at 11 m/s. The ball rebounds in the opposite direction with a speed of 6 m/s.
A: Obtain the angular speed of the bar just after collision.
B: During the collision, explain why is the angular momentum conserved but not the linear momentum?