  We report the results of a radial velocity survey of planetary nebulae (PNe)
located in the tidal features of the well-known interacting system NGC 5194/95
(M51). We find clear kinematic evidence that M51's northwestern tidal debris
consists of two discrete structures which overlap in projection -- NGC 5195's
own tidal tail, and diffuse material stripped from NGC 5194. We compare these
kinematic data to a new numerical simulation of the M51 system, and show that
the data are consistent with the classic ``single passage'' model for the
encounter, with a parabolic satellite trajectory and a 2:1 mass ratio. We also
comment on the spectra of two unusual objects: a high-velocity PN which may be
associated with NGC 5194's halo, and a possible interloping high-redshift
galaxy.
