Excellent - a good start to my day - thanks for sharing the source. I do some similar things but not yet with Greenfoot. I'll share back shortly - have you heard of github? On first run I wanted to get it to stop at the 0,90,180,270 degrees points . I have a feeling that I will use this working example for a demo that I want to do...

Good but I want to launch from one side and watch the trajectory as it goes to the other. The RHS seems blind. I'd love to see how you did this in Greenfoot, well done.