Whats the medium or average velocity of a meteor coming into earth's atmosphere? Is is about 30,000 mph? I guess a lot would depend on the exterior force that launched the rocks from the moon in the first place. The moon is roughly 240,000 miles from earth. So you could figure the math, I guess. And that's ballpark. Blacbird is correct about an object that size disintergrating before it hits the earth's surface. Composition of the object has much to do with it too. Lot's of variables here.
Tri
Escape velocity of Earth is about 7 miles per second, or about 25,000 miles per hour. That's about the speed the Apollo Moon missions re-entered Earth atmosphere, and I'd say that's a good number for anything sent from the Moon with just barely enough velocity to escape the Moon's gravity and come to Earth.
(Obligatory SF reference of regular shipments from Moon to Earth being repurposed as bombs: "The Moon is A Harsh Mistress," Robert Heinlein)
Low-Earth orbiting satellites such as the Shuttle come in at a slower speed of about 17,000MPH. Re-entry is also at a quite shallow angle, using the time in the atmosphere to slow down before it gets to Earth. A steeper angle will take less time to get to Earth, but may heat up faster because it gets to denser parts of the atmosphere sooner, perhaps contributing to it exploding into fragments that then completely burn up.
Rereading the OP, automobile-sized rocks lifted from the Moon could well burn up depending of course on composition.
The Earth orbits the Sun at 13 miles per second, or 47,000MPH. A meteor can hit Earth at any angle from any direction, but much debris orbits the same general direction with the planets, so I think they usually hit slower than that.
Composition surely has a lot to do with it. Being an almost all-steel automobile, I suspect something solid would be left to hit land (or ocean, depending on where it falls). The body would surely burn off, but larger metal parts such as the engine and frame may be protected by the body during early re-entry, and so not completely burn up.
The Space Shuttle Columbia is an interesting case. The remaining carbon wing edge and tiles protected much of it during early re-entry, and it was of course much larger than an automobile, and many chunks hit the ground. Quite surprisingly, an important component containing large amounts of data from the mission was recovered, a hard disk drive:
http://www.computerworld.com/s/arti..._i_hard_drive_data_recovered_from_crash_site_
So, then the objects in this case would be going only about 10K mph. Would that in itself make scientists (and therefore governments) go, "mmm that warrants further investigation. see if we can't pull up satellite images and backtrack where it came from..." or would they say, "pfft, ignore that! It might make for a neat lightshow over Tokyo, but don't cancel dinnerplans."
As I stated above, if they come from the Moon they'll be going at closer to 25kmph, and the higher-than-average speed for a near-Earth object may attract more attention. If they get enough info on the paths to discover that both objects came not from two random directions but from the direction of the Moon, scientific (and while I'm at it, military) eyebrows will certainly be raised.
Also, with these rocks taking days to make the journey (and especially going slowly through the 'sticking point' where the gravity of the Earth and the Moon is equal), a relatively small variation in the launch speed between them could cause a 12-hour difference between hitting Earth (or its atmosphere) even when hitting head-on, and than in itself would make them hit on opposite sides of the Earth.
