Question

About how fast is an asteroid going when it hits a planet?

Answer 1

Probably rather variable, but of magnitude similar to `50,000` meters per second.

Explanation:

I think it would be quite variable depending on the circumstances, but similar in order of magnitude to the speed with which the Earth orbits the sun.

Let's do a few rough calculations:

The Earth is roughly `9.3xx10^7` miles from the sun

So the length of the Earth's roughly circular path around the Sun is about `2 pi` times this, say `5.84xx10^8` miles.

The Earth travels this path in about `365` days, so the miles per day is about `(5.84xx10^8) / 365 = 1.6xx10^6` miles per day.

Divide by `24` to get miles per hour: `(1.6 xx 10^6) / 24 ~~ 67,000` miles per hour

To get meters per second multiply by `1609.344/3600` to get about `30,000` meters per second.

Compare this with the speed at which comet Shoemaker-Levy collided with Jupiter, which is estimated at `60,000` meters per second. So it seems we're in the right ballpark.