  We estimate ages and physical properties of powerful radio galaxies. An
analysis of new multi-wavelength VLA observations of eleven very powerful
classical double (FRIIb) radio galaxies with redshifts between 0.4 and 1.3 is
presented. We estimate ages and velocities for each side of each source. The
eleven new sources are combined with previously studied samples and the
characteristics of the full sample of 31 sources are studied; the full sample
includes sources with redshifts between 0.056 and 1.79, and core-hot spot sizes
of about 30 to 400 kpc. The velocities are independent of core-hotspot
separation, suggesting the rate of growth of a given source is roughly constant
over the source lifetime. We combine the rate of growth, width, and pressure of
a source to study the beam power, lifetime, energy, and ambient gas density
using standard methods previously applied to smaller samples. Typical beam
powers are in the range from 1E44 to 1E46 erg/s; we show that this quantity is
insensitive to assumptions regarding minimum energy conditions. The beam powers
are independent of core-hotspot separation suggesting that the beam power of a
given source is roughly constant over the source lifetime. Typical total source
lifetimes are found to be about a few E6 to E7 years, and typical total outflow
energies (E/c^2) are found to be about 5(E5 - E6) solar masses. Ambient gas
densities are found to decrease with increasing core-hotspot distance, but have
no redshift dependence. Overall, the results obtained with the sample of 31
sources studied here are consistent with those obtained earlier with smaller
samples.
