Not sure where to put this topic, here or Assemblies so I'll try both.

I read about a trebuchet simulation to teach CosmosMotion that flings a ball on a rope. The arm of the trebuchet pulls the rope that has a loop on one end that attaches to a hook. The ball is pulled through a trough untill it begins to become airborne. At a point of the arm's arc, the ball/rope disconnects from the hook and flies off into never/never land.

What I'm trying to figure out is how to set up the asembly mates, both how to keep the ball in the trough until it can fall out and the loop/hook that comes loose.

Any ideas?