posted by olga .
If an 75-kg baseball pitcher wearing frictionless roller skates picks up a 0.145-kg baseball and pitches it toward the south at 40 m/s, how fast will he begin moving toward the north?
Since there are no non-conservative forces involved in this scenario, you can use the principle of the conservation of momentum. Set up the momentum of the baseball player equal to the momentum of the baseball: (75kg)(vB)=(0.145kg)(40m/s). The velocity of the baseball player is 0.077 m/s north.