Rotation is really hard because it combines so many concepts, so this week is a break from new content and more about problem solving! The problem set contains a variety of tricky problems that involve rotational and/or dynamics concepts. Enjoy the following tricks below as well.
Idea: Rotational Impulse
In problems involving both rotation and translation, you can relate rotational and translational impulses with
$$\Delta L = r \Delta p.$$
Idea: Spools
The rate of unwinding of a spool rotating at $\omega$ (could be translating as well) is just $\omega R$, where $R$ is the radius of the spool.
Tip: Energy
When applying conservation of energy, be careful to not miss any components of energy. If an object is rotating and translating, make sure to include the rotational component of the energy -- even if $r$ is small, it may be significant as $\omega \sim 1/r$ (as we saw in that one problem in lecture).