  We study the dynamics of a dilute Bose gas at zero temperature following a
sudden quench of the scattering length from a noninteracting Bose condensate to
unitarity (infinite scattering length). We apply three complementary approaches
to understand the momentum distribution and loss rates. First, using a
time-dependent variational ansatz for the many-body state, we calculate the
dynamics of the momentum distribution. Second, we demonstrate that, at short
times and large momenta compared to those set by the density, the physics can
be well understood within a simple, analytic two-body model. We derive a
quantitative prediction for the evolution of Tan's contact, which increases
linearly at short times. We also study the three-body losses at finite
densities. Consistent with experiments, we observe lifetimes which are long
compared to the dynamics of large momentum modes.
