My favorite physics problem not is not an end-of-chapter problem

[CPW]

In physics pedagogy, the routine is to introduce new material in lectures and then practice the material in end-of-chapter problems. This problem, shown below, familiar to many of us on PF, is my favorite. One must get to intermediate mechanics class in undergraduate physics studies to finally see it, and once the mathematical steps are mastered, one may find the knowledge gained most satisfying. At least, that’s my experience:

I bet you can name the problem.

 

[malawi_glenn]

Kepler problem

 

[Office_Shredder]

Some sort of handwriting machine learning algorithm.