a 5kg chunk of ice is sliding at 12m/s on the floor of an ice-covered valley when it collides and sticks to another identical chunk of ice that is initially at rest. Assume that the ice surface is frictionless. After the collision, the ice blocks slide partially up a hillside and then slide back down. How fast are they moving when they reach the valley floor again? (Hints: break down this problem into two parts - the collision and the behavior after the collision)