The four-bar linkage shown in Figure 2.53 . The crank OA, the connecting rod AB and the rocker BC are 20 mm, 120 mm and 60 mm long, respectively. The crank rotates at a speed of 60 rpm and the centre distance OC is 90 mm. At the instant shown determine (a) the velocity of C, (b) the angular velocity of the rocker BC and (c) the angular velocity of the connecting rod AB.