It looks like your standard matchbox car loop. I need to find the minimum height h that will allow a solid cylinder of mass m and radius r_1 to loop the loop of radius r_2. "Express h in terms of the radius r_2 of the loop." I am not quite getting a certain portion of this. I know the important part of this problem is when the cylinder is at the top of the loop. Now, at this point, I know it has a potential energy of 2*r_2*m*g To stay on the track without slipping, I think I need v = R*omega At the top part of the track, the cylinder is upside down, and has no normal force... so weight matters? I may need to use this: K = 1/2Mv_cm^2 + 1/2 I_cm*omega^2 mgh = (2)r_2(mg) + KE? + ? I am a bit confused at this point. How am I suppose to put this together?