A 2.0-kg ball is attached to the end of a 2.5-m string to form a pendulum. This pendulum is released from rest with the string horizontal. The ball, at the lowest point in its swing when it is moving horizontally, collides inelastically with a 2.0-kg block initially at rest on a horizontal, frictionless surface. What is the speed of the ball-block system just after the collision?