  We investigate the total kinetic powers (L_j) and ages (t_age) of powerful
jets in FR II radio galaxies by comparison of the dynamical model of expanding
cocoons with observations. We select four FR II radio sources (Cygnus A, 3C
223, 3C 284, and 3C 219), for which the mass-density profiles of intracluster
medium (ICM) are known in the literature. It is found that large fractions >
0.02 - 0.7 of the Eddington luminosity (L_Edd) are carried away as a kinetic
power of jet. The upper limit of estimated 2 L_j / L_Edd are larger than unity
(< 10) for some sources, suggesting a possibility of super-Eddington mass
accretions. As a consequence of the large powers, we also find that the total
energy stored in the cocoon (E_c) exceeds the energy derived from the minimum
energy condition for the energy of radiating non-thermal electrons and magnetic
fields (E_min): 4< E_c /E_min <310. This implies that most of the energy in
cocoon is carried by invisible components such as thermal leptons (electron and
positron) and/or protons.
