[单选题]
You (50-kg mass) skate on irl 8i53r +wogfce at 4.0 m/s to greet your frienx0kq ox/2 dfn;d (40-kg mass), who is standing still, with open arkx nf; q2/0dxoms. As you collide, while holding each other, with what speed do you both move off together?
