There's a light gas gun at NASA Ames that routinely shoots models with a muzzle velocity of 5 km/sec. It's 40 year old technology. They can get relative velocities of 10 km/sec by shooting a model into a slug of test gas shot out of a 16 inch shock tube. Test time is a bit short doing it that way so it's hardly done anymore.

Your typical zillion ton asteroid is going to whack into Mars at >15 km/sec. Escape velocity from Mars is in the ballpark of 7 km/sec (too lazy to calculate the exact value). There's heaps of momentum from the original asteroid for flinging 100 kilogram rocks into escape trajectories. This is a non-issue.

Gary