  We investigate the total kinetic powers (L_{j}) and ages (t_{age}) of
powerful jets of four FR II radio sources (Cygnus A, 3C 223, 3C 284, and 3C
219) by the detail comparison of the dynamical model of expanding cocoons with
observed ones. It is found that these sources have quite large kinetic powers
with the ratio of L_{j} to the Eddington luminosity (L_{Edd}) resides in $0.02
<L_{j}/L_{Edd} <10$. Reflecting the large kinetic powers, we also find that the
total energy stored in the cocoon (E_{c}) exceed the energy derived from the
minimum energy condition (E_{min}): $2< E_{c}/E_{min} <160$. This implies that
a large amount of kinetic power is carried by invisible components such as
thermal leptons (electron and positron) and/or protons.
