If a meteorite were to crash into the earth, what would the predicted speed be in miles per hour?

Question: If a meteorite were to crash into the earth, what would the predicted speed be in miles per hour?
- Keywords:
  earth,
  meteorite,
  speed
Asked by balletshoes1998 to Adam, Catherine, Karen, Leila, Nazim on 15 Mar 2012.
- Adam Stevens answered on 14 Mar 2012:
  
  There’s a lot of factors that affect this.
  
  The worse case would be if the meteorite came from the opposite direction to the way Earth is moving. In that case the impact speed would be the speed of Earth’s movement PLUS the speed of the meteorite itself. A slower case would be if the Meteorite came up from behind us, in which case it would the speed of Earth’s movement MINUS the speed of the meteorite.
  
  Typically the meteorites we know about have a speed of anything from 10 to 100km/sec when they reach our atmosphere. They quickly get slowed down by friction with the air though, and can even get down to 0km/sec when they reach the ground!
  
  We can calculate how fast the meteorites that made big craters were going, and some could have still been going about 10km/sec when they hit the ground, which is pretty fast!
- Leila Battison answered on 15 Mar 2012:
  
  Meteors (and other things in space) tend to go faster when they are closer to a big object like the sun, or very close to a planet. So it could actually speed up as it gets closer to us!
  
  Out in space, but near to the sun, meteors have been seen that travel nearly 100,000 miles an hour, but when the earth and the meteor are rushing towards eachother, they can get a combined speed of an incredible 160,000 miles an hour. That’s over 200 times the speed of sound!
  
  It slows down in the atmosphere because of friction with the air (thats why we see them burning as shooting stars) but the atmosphere isn’t thick enough to slow it down very much, so a big meteorite is going to make a really really big crash!
- Karen Masters answered on 18 Mar 2012:
  
  Well that would depend on two things (1) the mass of the rock about to hit and (2) it’s orbit. It might be sort of going the same way as Earth and so not moving that fast with respect to us, or it could be going backwards (more unlikely I think) and hit really really fast. It matters a lot actually – because the energy of something moving fast goes like it’s mass times its speed squared – so double the speed, four times the energy…..
- Nazim Bharmal answered on 19 Mar 2012:
  
  It depends on how big the asteroid was and how fast it was going when it hit the atmosphere and at what angle. The quickest that it is likely to go is a few km/s which means you wouldn’t have time to hear it hit the ground, you’d just see a bright streak in the sky and then feel the impact.