A solid spherical ball is rolling on a frictionless horizontal plane surface about its axis of symmetry. The ratio of rotational kinetic energy of the ball to its total kinetic energy is\\
(1) $\frac { 1 } { 5 }$\\
(2) $\frac { 2 } { 5 }$\\
(3) $\frac { 2 } { 7 }$\\
(4) $\frac { 7 } { 10 }$