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An electric sander consisting of a rotating disk of mass 0.75 kg and radius 10 cm...

An electric sander consisting of a rotating disk of mass 0.75 kg and radius 10 cm rotates at 15 rev/sec. When applied to a rough wooden wall the rotation rate decreases by 30.0%.

a) What is the final rotational kinetic energy of the rotating disk?

b) How much has its rotational kinetic energy [in J] decreased?

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