A uniform sphere with mass M and radius R is rotating with angular speed wi about a frictionless axle along a diameter of the sphere. The sphere has rotational kinetic energy K1. A thin-walled hollow sphere has the same mass and radius as the uniform sphere. It is also rotating about a fixed axis along its diameter. In terms of wi, what angular speed must the hollow sphere have if its kinetic energy is also K1, the same as for the uniform sphere? Express your answer in terms of wi.