You (50 kg mass) skate on ice at 4.6 m/s to greet your friend (54 kg mass), who is standing still, with open arms. As you collide head-on, while holding each other, with what speed do you both move off together?

Use conservation of momentum to find the final velocity:

m_1 v_1 + m_2 v_2 = (m_1+m_2)v_f