3. A solid uniform semi-circle with radius R is placed along the x axis, with its axis of symmetry along y axis. (a) Where is the center of mass of the semi-circle, in coordinate form? (b) If the semi-circle begins spinning in a clockwise direction around the origin, speeding up at a constant rate, what is the direction of the angular velocity? the angular acceleration? (c) As the semi-circle speeds up, describe how the total linear acceleration changes.