1. The problem statement, all variables and given/known data Rigid body The plane rigid body ABCD shown in the figure has rectangular shape and slides along the orthogonal runners X, Y. The points A and B are always in contact with the ranners. Data: ω=3 rad/s (angular velocity counterclockwise); [itex]\Theta[/itex]=30°; AB=CD=1m; AD=CB=0.5m. Determine: The A and C velocities; The position of instantaneous rotation center; The value of [itex]\Theta[/itex] for which the horizontal velocity component of D is null. 2. Relevant equations Fundamental geometric identities 3. The attempt at a solution Without knowing the center of rotation or the relevant velocities a priori I don't know how one can be solved for the other. So really, I can't make it past the first step. The instructor gave us this solution which to me makes no sense. He claims that Va = Va/b + Vb and that Va/b = ω*AB But this makes no sense since it assumes the center of rotation is at point B, or else Va/b wouldn't be given as the product of ω times the length of segment AB. Am I missing something or did the instructor forget to inform us that ω refers to point B?