I used some time to understand why Anna is taking AP Physics and to understand why she felt that she didn't want to take the AP exam. Then, we started to look at the workbook examples of harmonic motion of a cart on a horizontal track with a spring attached to a fixed point. I felt that she was not totally following the example so I brought up the motion of a roller coaster moving under the combination of gravity and kinetic energy. I then showed her how the cart on a horizontal track attached by a spring is acting under elastic potential energy instead of gravitatinal potential energy. I reminded her of mechanical energy which has the same total energy at all times. There was no assignment.