A small block on a frictionless, horizontal surface has a mass
of 0.0250 kg. It is attached to a massless cord passing through a
hole in the surface. The block is originally revolving at a
distance of 0.300 m from the hole with an angular speed of 1.75
rad/s. The cord is pulled from below, shortening the radius of the
circle in which the block revolves to 0.150 m. Model the block as a
point particle. (a) Is the angular momentum of the block conserved?
Why or why not? (b) What is the new angular speed? (c) Find the
change in kinetic energy of the block. (d) How much work was done
in pulling the cord?