Earlier quoted context omitted.
If you're going any slower than 40 km/h the only thing you'll be doing in a terrain park is falling on your face. This [1] cable-driven terrain park "for children and adults" pulls you at 40 km/h. If you're looking at landing anything bigger than a 360 you'll need to be going closer to 60 km/h. Ski racers are not happy until they're going (a lot) faster than 90. [1] http://www.al.no/en/html/aktiviteter/vinter/ski_sno…
I'm a level 3 snowboard instructor in Canada, and I would say I infrequently go over 40km/h. It's only when I stand still on a groomer and "go fast", or for the run-in for the L/XL jumps.
The pull rope I linked above is for kids with small/medium jumps, and that's 40 km/h.