A 18. Two rolling golf balls of the same mass collide. The velocity of one ball is initially 2.70 n1;r s [B]. After the collision, the velocities of the balls are 2.49 m! s [62.8" N of W] and 2.37 mfs [159.2D S of E]. What are the magni- tude and direction of the unknown initial velocity? 19. A 0.25-kg ball is attached to a 26-cm piece of string (Figure 2). The ball is first raised so that the string is taut and horizontal, then the ball is released so that, at the bottom of its swing, it undergoes an elastic head- on collision with a 0.21-kg ball that is free to roll along a horizontal table. (a) What is the speed of the swinging ball just before the collision? (b) What is the speed of the 0.21-kg ball just after the collision? 0.25 kg : stn'ng /5UPPC"'t 20. A large ball of modelling clay of mass 4.5 X 102 g is rolled on a tabletop so that it collides with a stationary small wooden box of mass 7.9 X 102 g. The collision is completely inelastic, and the ball and box then slide on the table for a distance of 5.1 cm. If the speed of the ball is 2.2 mls just before the collision, determine (a) the speed of the ball and box just after the collision (b) the magnitude of the friction force acting on the ball and box