[McGruff]

Looks like IMUS was a little low:

Investigators searching for clues to Columbia's loss are focusing on a 2 1/2-pound, 20-inch chunk of foam insulation that fell from the shuttle's external tank moments after liftoff and stuck the underside of the wing, possibly damaging the tiles. The shuttle was traveling at 2 1/2 times the speed of sound at the time, or just over 1,900 mph.

from this article here.

[leadpenny]

That puts it at approx. 2800 fps. As I remember that is about the muzzle velocity of the average high powered rifle. Anything solid in that foam and it could do some real damage.