1. A steel ball of mass 0.400 kg is fastened to a cord 60.0 cm long and fixed at the far end, and is released when the cord is horizontal. At the bottom of its path, the ball strikes a 2.00 kg steel block initially at rest on a frictionless surface. The collision is elastic. Assuming the positive direction is to the right, find, just after the collision, Velocity of the ball Velocity of the block I don't know how to start this one, never the less do it. 2. A body of mass 2.4 kg makes an elastic collision with another body at rest and continues to move in the original direction but with one-fourth of its original speed. The struck block has a mass of 1.44kg. What is the speed of the two-body center of mass if the initial speed of the 2.4 kg body was 4.5 m/s? I plugged in the numbers into the equation (m1v1+m2v2)/(m1+m2) and got 3.234375 which I know is wrong. Don't even know how I got v2.