text: Treat this problem as a point source of mass on a massless arm.\nMass (m) = 4 * 78 kg = 312 kg\nArm length (radius, r) = 1.2 m\nForce (F) = 66 N\n\nMoment of inertia = m*r^2 (kg-m^2) = 312 * 1.2 * 1.2 = 449.28 kg-m^2\n\nFrom Wikipedia; http://en.wikipedia.org/wiki/Moment_of_inertia:\n"The (scalar) moment of inertia of a point mass rotating about a known axis is defined by\n    I = m * r^2\nwhere,\n    m is its mass,\n    and r is its perpendicular distance from the axis of rotation."\n\nAngular acceleration (α)= τ/I = (F * m)/I = (66 * 1.2)/ 449.28 = 0.176 rad/sec^2\n\nFrom Wikipedia; http://en.wikipedia.org/wiki/Angular_acceleration\n"   α = τ/I (rad/sec^2)\nwhere,\n   τ is torque\n   I is moment of inertia. "\n\nHope this helps!