Gavin Francis asked:
If you had been riding through space on the asteroid that killed the dinosaurs, would you have been able to jump off it, before it hit the Earth?
Transcript to follow...
Assuming the asteroid was travel at 50KM/s you would have to accelerate to that speed in the reverse direction in the second or so when it reaches the fringes of the atmosphere so that you can deploy your parachute.
If one plans ahead, then YES.
Jumping off an asteroid is no big deal as its gravitational pull would be small. But in the absence of any other heavenly bodies your combined center of mass would continue to accelerate earthwards, so in order not to participate in the extinction event, you would have to jump away from the earth at or above escape speed. Whilst this would exonerate you from the evolution of mankind in your own mind, it would however bring forward the date of extinction by accelerating the asteroid earthwards, and incur the wrath of treehuggers. alancalverd, Wed, 25th Dec 2013
The gravity of a 10km asteroid would be very low. It should be possible for an unassisted human to reach escape velocity away from this asteroid, at 1-2 meters/second.
I finally had time to run the numbers (always a mistake to do it after writing an answer!).
Escaping from the asteroid isn't a problem. The trouble is that you are already accelerating towards earth in the earth's gravitational field, so you need to escape from that too. alancalverd, Sat, 28th Dec 2013
To slow down sufficiently to enter the Earths atmosphere at such a speed that you could deploy a parachute you would have to accelerate away from the asteroid at something like 5000g which would be neither practical or healthy.
Dominic does say in his answer that, although you'd be travelling in an Earth-bound direction and at a velocity of some kilometres per second, if you jumped off far enough from Earth, you'd also have a vector at ninety degrees to the asteroid trajectory, so you could, theoretically time your jump so you'd sail past Earth rather than hit it. How you'd stop again, or avoid disappearing off into outer space, is another matter...! chris, Sun, 29th Dec 2013