Solve the below problem:
Q: A half-cylinder of mass m and radius r is released from rest in the position shown. Knowing that the half-cylinder rolls without sliding, determine
(a) Its angular velocity after it has rolled through ugh 90°,
(b) The reaction at the horizontal surface at the same instant.
![1140_Half cylinder.jpg](https://secure.tutorsglobe.com/CMSImages/1140_Half cylinder.jpg)