Answer to Question #263217 in Physics for haze

Question

There are two ice skaters with mass 80 kg and 32 kg at rest on ice initially. When one of them (heavier skater) pushes off against the other (lighter skater), and the heavier skater starts to move with a speed of 3 m/s. What is the speed of the lighter skater in m/s? Note that the distinguish the positive direction from the negative direction, and the heavier skater moves in the positive direction.

Answer 1

According to momentum conservation:

$$0=mv+Mu,\\\space\\ v=-Mu/m=-80·3/32=-7.5\text{ m/s}$$

(-7.5 m/s in the direction opposite to the direction of motion of the 80-kg skater).