  The Hydra $N$-body hydrodynamics code has been modified to model, from the
end of the Sedov phase, the effects of supernovae on the surrounding medium.
The motivation is to investigate the feedback of energy into the
interstellar/intergalactic medium. We compare our results for supernova
remnants (SNRs) in a uniform medium to previous detailed work on the late
evolution of SNRs. The code is found to reproduce the bulk characteristics of
SNRs well. Results on the effects of a single central SNR on Plummer clouds are
presented. The feedback of kinetic energy and the percentage mass loss can be
parameterised in terms of the cloud mass and characteristic radius in a simple
way. The kinetic energy fraction returned to the ISM from a SNR is $<3$ per
cent. The removal of gas from the cold, dense phase and the addition of energy
due to the lowering of the potential energy of a cloud is at least as
significant, if not much more so, than the kinetic energy leaving a cloud.
