We started by talking about impulse. It is notated using the letter J, not the letter I. In the context of chapter 9, I was the momentum of inertia which has a similar role that mass does for linear motion for rotational motion.
Figuring out the situation of what is going on in a problem can be the most difficult thing. Many times a diagram will help. Thinking about the directions of things can also be useful in getting started. For example with a sliding block and a horizontal restoring force. Also, you can often do problems in several different ways. With the spring and friction, conservation of energy was problem the easiest route.
The other problem had a summation of torques and figuring out the moment of inertia. One mistake would be to not take into account the torque due to the ladder, which can be thought of as a point mass at the center.