Use the definition of rotational kinetic energy. First, to find Earths rotational KE use it when I is its moment of inertia with respect to Earth's axis of rotation. Next to find the orbital know that the center of mass of the Earth-Sun system is so close to the center of the Sun and the Earth-Sun distance so large that we can use the Earth-Sun distance as the separation of their centers of mass and assume each to be a point mass. Then the moment of inertia can be found by treating the Earth as a point mass rotating about the sun. Lastly, compare the ratio of rotational kinetic energies.

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