Halliday, Resnick & Walker — Rotation: Problem Problem_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 10.25 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 \(70\text{ kg}\), 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 \(h = 1.4\text{ m}\)?