Finding Angular Speed and the Change in Kinetic Energy

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Homework Statement
A student sits on a rotating stool holding two
4 kg objects. When his arms are extended
horizontally, the objects are 0.9 m from the
axis of rotation, and he rotates with angular
speed of 0.63 rad/sec. The moment of inertia of the student plus the stool is 8 kg m2
and is assumed to be constant. The student
then pulls the objects horizontally to a radius
0.27 m from the rotation axis.
Calculate the final angular speed of the
student.
Answer in units of rad/s.


Calculate the change in kinetic energy of the
system.
Answer in units of J.
Relevant Equations
Finding Angular Speed and Change in Kinetic Energy
(4+.9)(Wf)=(4+.63)(.27)
(4.9)(Wf)=1.2501
Incorrect
 
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Your strategy for solving the problem is incomprehensible. I will not ask you to explain it, but I will ask you to consider what quantity is conserved in this case.
 
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