This problem was
suggested by Toby Crisford.
Two balls of equal radius and mass, free to roll on a horizontal plane, are
separated by a distance L large compared to their radius. One ball is solid, the
other hollow, and they are attracted by a mysterious force. How far will the
solid ball roll before it collides with the hollow ball?
Solutions (listed by author)
Gottlieb (html, 3k)