http://en.wikipedia.org/wiki/Electromagnetic_gun" [Broken] about rail guns says: the U.S. Navy has tested a railgun that accelerates a 3.2 kg (7 pound) projectile to approximately 2.4 kilometres per second (5,400 mph). It also talks about current research to use this technology to launch things...
Another may of looking at it, but reiterating what the others have said, is as follows:
F=dp/dt (Newton's second law states force equals rate of change of momentum)
=mdv/dt +vdm/dt (equation 1)
if the mass is constant then the rate of change of mass, dm/dt=0 so this becomes...