A string is wrapped around a disk of mass m = 2.3 kg and radius R = 0.09 m. Starting from rest, you pull the string with a constant force F = 8 N along a nearly frictionless surface. At the instant when the center of the disk has moved a distance x = 0.16 m, your hand has moved a distance of d = 0.23 m. (a) At this instant, what is the speed of the center of mass of the disk? vcm = m/s (b) At this instant, how much rotational kinetic energy does the disk have relative to its center of mass? Krot = J