1. The problem statement, all variables and given/known data Consider a spere with momenta of inertia of 2/5*m*r^2 that rolls down a plane surface (no friction). I want to calculate the rotational energy of the sphere when it has speed v0. 2. Relevant equations Erot=1/2*I*w^2 3. The attempt at a solution My only problem is: Do I need to transform my I=2/5*m*r^2 with the rule of steiner, or don't I have to use the rule of Steiner? I would say no.