Halliday, Resnick & Walker — Rotation: Problem 54

54 In a judo foot-sweep move, you sweep your opponent’s left foot out from under him while pulling on his gi (uniform) toward that side. As a result, your opponent rotates around his right foot and onto the mat. Figure 10-35 shows a simplified diagram of your opponent as you face him, with his left foot swept out. The rotational axis is through point O. The gravitational force $\vec{F}_g$ on him effectively acts at his center of mass, which is a horizontal distance $d = 28\text{ cm}$ from point O. His mass is $75\text{ kg}$, and his rotational inertia about point O is $65\text{ kg}\cdot\text{m}^2$. What is the magnitude of his initial angular acceleration about point O if your pull $\vec{F}_a$ on his gi is (a) negligible and (b) horizontal with a magnitude of $300\text{ N}$ and applied at height $h = 1.4\text{ m}$?