A small block on a frictionless surface has a mass of 50 g. It is attached to a massless string passing through a hole in a horizontal surface. The block is originally rotating in a circle of radius 35 cm with angular speed 0.90 rad/s. The string is then pulled from below until the radius of the circle is 20 cm. You may treat the block as a point particle.
(a) Is the angular momentum of the block conserved? Why or why not?
(b) What is the final angular speed?
(c) What are the initial and final tensions in the string?
(d) What was the change in kinetic energy of the block?