In the figure the lower disk, of mass 450 g and radius 4.0 cm , is rotating at 180 rpm on a frictionless shaft of negligible radius. The upper disk, of mass 280 g and radius 2.2 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. Find the common speed.Express your answer in revolutions per minute.Find the fraction of the initial kinetic energy lost to friction.Express your answer as a percentage.