1. The problem statement, all variables and given/known data I really don't understand what to do next. A wheel is rotating freely with an angular speed of 950rev/min on a shaft whose rotational inertia is negligible. A second wheel, initially at rest and with twice as much rotational inertia of the first is suddenly coupled on the shaft. What is the new angular speed? 2. Relevant equations 3. The attempt at a solution No external torques, so conservation of momentum must be observed. I is the rotational inertia of the wheel spinning at 950rev/min; 2I is the rotational inertia of the wheel that is coupled. wf is the final angular speed. Iw = (I + 2I)wf wf = Iw/(3I) wf = w/2I Right? I can substitute w in, but nothing to substitute in for I. How do I solve this problem?