  The transient response of a quantum dot with strong Coulomb interaction to a
fast change in the gate potential, as well as the stationary ac-response to a
slow harmonic variation of the gate potential are computed by means of a
real-time diagrammatic expansion in the tunnel-coupling strength. We find that
after a fast switching, the relaxation of charge and spin are governed by a
single time constant each, which differ from each other due to Coulomb
repulsion. We compare the response to a step potential with the $RC$ time
extracted from the ac response.
