Hollow sphere, angular momentum, torque problem? help?? a hollow sphere or radius 0.15m with rotational inertia = 0.040 kg m^2 about a line through its center of mass, rolls without slipping up a surface inclined 30 degree to the horizontal. at a certain initial position,the sphere's total kinetic energy is 20J. a) How much of this initial KE is rotational? what i did Hollow sphere = 2/3MR^(2) KErot = 1/2 Iω^2 KEtotal = KEtranslational + KErotational a) 20 = 1/2mv^2 + 1/2 x 2/3 mr^2 20 = 1/2mv^2 + 1/3 mr^2 this part confuses me 1/2mv^2 + 1/3 mr^2 = 5/6mv^2 20 = 5/6mv^2 How was 1/2mv^2 + 1/3 MR^2 = 5/6mv^2?? mv and MR are different yet how were they both added together??