A thin, uniform, metal bar, 3 m long and weighing 90 N, is hanging vertically from the ceiling by a frictionless pivot. Suddenly it is struck 1.3 m below the ceiling by a small 3 kg ball, initially traveling horizontally at 12 m/s. The ball rebounds in the opposite direction with a speed of 7 m/s.
A) Find the angular speed of the bar just after the collision.
B) During the collision, why is the angular momentum conserved but not the linear momentum?