Two ice skaters stand facing each other at rest on a frozen pond. They push off against one another and the 48 kg skater acquires a speed of 0.69 m/s. If the other skater acquires a speed of 0.87 m/s, what is her mass in kilograms?

38 kg

Explanation:

Newton's Third Law tells us that if skater 1 exerts a force on skater 2 then skater 2 exerts an equal but opposite force on skater 1. Since ΔP = FΔt then the change in momentum of both must also be equal since the the magnitude of the force they experience is also equal.

change in momentum of skater 1 = change in momentum of skater 2

48 kg * (0.69 m/s - 0 m/s) = m * (0.87 m/s - 0 m/s)

m = 38 kg