A little over six years ago, I blogged about Io's volcanoes and how fast the material that comes out of them is exiting the volcanoes.
Io is one of the moons of Jupiter.
Using the gravity of Io and how high the plumes go, I calculated (using the equation above) that the material must exit the volcanoes at 1,075 meters per second (or 1.075 km/s) to reach the altitude they do (as high as 200 miles over the surface of the moon). And, according to Wikipedia, the correct figure is 1 km/s. Or 2,236 miles per hour. That's pretty fast. Faster even than Enceladus.
But what I was glad about, what that my calculations six years ago were mostly confirmed. The source Wikipedia used might have rounded down to one significant figure and if I do that, I get the same answer (1 km/s).