1. The problem statement, all variables and given/known data Hi all! I'm working on a dynamics homework and have hit a wall here: "If the frictional moment at the pivot O is 2 N m, determine the angular acceleration of the grooved drum, which has a mass of 8 kg and a radius of gyration k = 225 mm. Ans: α = 0.622 rad/s^2 " 2. Relevant equations M = m g r ƩM = I α I = m k^2 3. The attempt at a solution The two masses exert moments about O, so my first step is to sum the moments about the pivot O: ƩM = (12 kg)(9.81 m/s^2)(0.2 m) - (7 kg)(9.81 m/s^2)(0.3 m) ƩM = 2.943 N m These moments are resisted by the frictional moment such that: ƩM = (2.943 N m) - (2 N m) ƩM = 0.943 N m Next we need the moment of inertia of the pulley: I = m_pulley * k^2 I = (8 kg)(0.225 m)^2 I = 0.405 kg m^2 Finally we can solve for angular acceleration: ƩM = I α so α = ƩM / I α = (0.943 N m) / (0.405 kg m^2) α = 2.33 1 / s^2 My analysis seems reasonable and I come up with the right units, but it is not very close to the given answer. Am I doing something wrong?