I can't figure out this problem. Pretty much totally lost. It has a hollow, spherical shell with a mass of 2kg, rolls without slipping down an incline of 38 degree's. It wants me to find the acceleration, the friction force, ane the minimum coeffcient of friction needed to prevent slipping. The examples in my book and the equations all seem to have the Radius in them, and my problem doesn't give a radius. The equation that is has is Vcm=Rw. So i'm not sure what to do when I don't have the radius and only the mass. Since is says it is a hollow sphere, am I supposed to do something with the motion of inertia ? With K=1/2Mv^2+1/2Iw^2 ? And then I don't know how I'm supposed to find the frictional force and the coeffcient of friction. g(sinθ-μcosθ)=a ?