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In the figure the lower disk, of mass 440 g and radius 3.7 cm , is...

In the figure the lower disk, of mass 440 g and radius 3.7 cm , is rotating at 180 rpm on a frictionless shaft of negligible radius. The upper disk, of mass 280 g and radius 2.0 cm , is initially not rotating. It drops freely down onto the lower disk, and frictional forces bring the two disks to a common rotational speed. A) Find the common speed. B) Find the fraction of the initial kinetic energy lost to friction.

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