Rotational energy of sphere $E_{R}=\frac{1}{2} I \omega^{2}$ For sphere, moment of inertia $I =\frac{2}{5} m R^{2}$ $\therefore E_{R} =\frac{1}{2}\left(\frac{2}{5} m R^{2}\right)\left(\frac{v}{R}\right)^{2}$ $=\frac{1}{5} m v^{2}$ Translational kinetic energy $E_{r}=\frac{1}{2} m v^{2}$ $\therefore$ Total energy $=\frac{1}{5} m v^{2}+\frac{1}{2} m v^{2}$ $=\frac{7}{10} m v^{2}$ $\therefore$ Required fraction $=\frac{\frac{1}{5} m v^{2}}{\frac{7}{10} m v^{2}}$ $=\frac{2}{7}$
The system of particles refers to the extended body which is considered a rigid body most of the time for simple or easy understanding. A rigid body is a body with a perfectly definite and unchangeable shape.
The distance between the pair of particles in such a body does not replace or alter. Rotational motion can be described as the motion of a rigid body originates in such a manner that all of its particles move in a circle about an axis with a common angular velocity.
The few common examples of rotational motion are the motion of the blade of a windmill and periodic motion.