A thin uniform metal bar, 2m long and weighing 90N, is hanging vertically from the ceiling on a frictionless pivot. Suddenly, it is struck 1.5m below the ceiling by a small 3kg ball, intially travelling horizontally at 10m/s. The ball rebounds in the opposite direction with a speed of 6m/s.
Find the angular speed of the bar after the collision.
I am struggling to find the right energy/conservation equation to use. I know it is to do with the conservation of angular momentum, but i cannot see how to use the fact that the small ball rebounds with a speed 6m/s in my equation.