  We simulate the motion of a massive object through a dilute Bose-Einstein
condensate by numerical solution of the non-linear Schr\"odinger equation
coupled to an equation of motion for the object. Under a constant applied
force, the object accelerates up to a maximum velocity where a vortex ring is
formed which slows the object down. If the applied force is less than a
critical value, the object becomes trapped within the vortex core. We show that
the motion can be described using the time-independent quantum states, and use
these states to predict the conditions required for vortex scattering.
