1. The problem statement, all variables and given/known data Two spheres look identical and have the same mass. However, one is hollow and the other is solid. Describe an experiment to determine which is which. 2. Relevant equations mgh= ½ m v^2 + ½ I ω^2 where I= 2/3 mr2 for a hollow sphere I=2/5 mr2 for a solid sphere 3. The attempt at a solution You could allow the two spheres to roll an identical incline from rest. For both spheres, the gravitational potential energy will be transformed to both rotational kinetic energy and translational potential energy when they reach the base. Since a solid sphere has a smaller moment of inertia, it is less resistant to rotation. More of the original gravitational potential energy will be converted into rotational potential energy for the solid sphere than for the hollow sphere. Thus, the hollow sphere must have more translational kinetic energy and will reach the bottom at a greater translational velocity than the solid sphere will. Logically I believe that the solid sphere should go faster.. so I am not confident in my logic above. Could you also argue that the at the moment released from rest the solid sphere will begin to rotate to fall down the incline before the hollow sphere due to the differences in inertia?