A small block on a frictionless horizontal surface has a mass of 2.50×10−2 . It is attached to a massless cord passing through a hole in the surface. (See the figure below .) The block is originally revolving at a distance of 0.300 from the hole with an angular speed of 1.75 . The cord is then pulled from below, shortening the radius of the circle in which the block revolves to 0.150 . You may treat the block as a particle. (a) Is 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?
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