# Sample Problem

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**Sample Problem**

Two skaters collide and embrace, in a completely inelastic collision. Thus, they stick together after as suggested.

(a) What is the velocity V of the couple after they collide?

SOLUTION: One Key Idea here is the assumption that the two skaters form a closed, isolated system.

(b) What is the velocity of the center of mass of the two skaters before the collision and after the collision?

SOLUTION: For the situation after the collision, we use the Key Idea that because the skaters are stuck together, their center of mass must travel with them.