Asmall block on a frictionless horizontal surface has a mass of 2.00×10?2 kg . I

Question

Asmall block on a frictionless horizontal surface has a mass of 2.00×10?2 kg . It is attached to a massless cord passing through a hole in the surface. (See the figure below (Figure 1) .) The block is originally revolving at a distance of 0.285 m from the hole with an angular speed of 1.75 rad/s . The cord is then pulled from below, shortening the radius of the circle in which the block revolves to 0.165 m . You may treat the block as a particle.   Is angular momentum conserved?   What is the new angular speed? Find the change in kinetic energy of the block.   How much work was done in pulling the cord?

Explanation / Answer

angular momentum will be conserved about that point

0.02 *0.285 ^2 *1.75 = 0.02*0.165^2 *w

w=5.22107438017 rad/s

change in KE =work done = -0.5* 0.02* (1.75*0.285)^2 + 0.5* 0.02* (5.22107438017*0.165)^2 = 0.00493391528

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