Question: Two light cylinderical cans roll down an inclined slope. One is filled with water, which may be assumed to act without friction, the other is filled with ice which sticks to the insides of the can. Which attains the higher speed and by what factor? Solution: The maths of this scenario is straight forward but I don't know how to distinguish between the two cans. I know that I either have to consider one rolling while the other skids thus I deal with rotational and kinetic energies or I have to consider different moments of inertia. Can one of them be considered hollow or does one skid instead of roll and more inmportantly why for either? Thanks.