If we have a ball rolling down from inclined roof that has bottom part at certain height about the ground. I want to know where does the ball land after it leaves the roof. So at this point potential energy is transfered to kinetic (rotational + translational). My question is: What is the expression I derive an initial velocity from? Is it EK(transl) or EK(transl)+EK(rot)? I think it should be only EK(transl), because I'm interested only in motion of a centre of mass, right? BUT, exercises in my book always counts with EK(rot), so I'm pretty confused. Can you please make it little more clear to me??