1. The problem statement, all variables and given/known data This is a solved problem I am trying to understand, I have attached the problem. 2. Relevant equations 3. The attempt at a solution In the solution of i), I don't understand why is it ok to apply the torque equation about O. The question does not state that block does not slide before toppling and ##\tau=I\alpha## can be applied only about CM or a fixed point, right? Its been quite some time I have done these kind of problems, I am very sorry for any silly questions. Any help is appreciated. Thanks!