Walker, Halliday & Resnick — Rotation: Problem 39

39 A wheel with a rotational inertia of $0.50\text{ kg}\cdot\text{m}^2$ about its central axis is initially rotating at an angular speed of $15\text{ rad/s}$. At time $t = 0$, a man begins to slow it at a uniform rate until it stops at $t = 5.0\text{ s}$. (a) By time $t = 3.0\text{ s}$, how much work had the man done? (b) For the full $5.0\text{ s}$, at what average rate did the man do work?