Problem: An amusement park ride consists of two seats (containing people) connected by a shaft which is pivoted at the center. (To solve real problems, we often have to simplify to make a first approximation before building a model for testing. We shall assume that the shaft is a thin rod of mass 250 kg and length 7.5 m; we'll approximate each seat and person as a sphere of mass 140 kg and radius 1.7 m.) Find the angular momentum of the system if it rotates at 18 rpm.

Solution: The angular momentum about the z-axis is the moment of inertia times the angular velocity: