How fast was comet Shoemaker-Levy 9 going when it hit Jupiter?
Comet Shoemaker-Levy 9 was travelling at a speed of about 60 km/s when it hit Jupiter.
Shoemaker-Levy 9 was a comet that was trapped in Jupiter's Orbit and the tidal forces from Jupiter's gravity caused the comet to break apart into 21 fragments, some as large as 1.2 miles (2 km) in diameter.
Animated GIF of Shoemaker-Levy 9:
GIF from: http://cse.ssl.berkeley.edu/SegwayEd/lessons/cometstale/commhhe_v2.html
The fragments eventually collided with the planet in the Southern Hemisphere between 16 July 1994 and 22 July 1994 at a speed of 60 km/s which is 134 000 miles/hour or 216 000 km/h.
The impact scars were more visible than the Great Red Spot storm for many months after impact:
Image from: http://hildaandtrojanasteroids.net/A1504-15apr11.html
Hope I helped :)