Solution: A horizontal platform in the shape of a uniform disk (I = 1/2 MR  2 for an axis at its center) is rotating without friction about a vertical axis at its center. The platform has mass 8.00 kg and radius 0.400 m. The platform is initially rotating at an angular velocity of 0.300 rev/s. Then a small bag of sand with mass 6.00 kg is dropped from a small height onto the platform at its rim. The bag of sand can be treated as a point mass. What is the final angular velocity of the platform after the bag of sand has been dropped onto it?

Problem

A horizontal platform in the shape of a uniform disk (I = 1/2 MR  for an axis at its center) is rotating without friction about a vertical axis at its center. The platform has mass 8.00 kg and radius 0.400 m. The platform is initially rotating at an angular velocity of 0.300 rev/s. Then a small bag of sand with mass 6.00 kg is dropped from a small height onto the platform at its rim. The bag of sand can be treated as a point mass. What is the final angular velocity of the platform after the bag of sand has been dropped onto it?