Work Step by Step
The momentum of the astronaut-wrench system is initially zero. If she throws the wrench but holds onto it, she’ll momentarily jerk backwards, but come to rest again just as the wrench does. If the astronaut throws a wrench directly away from the station, she will move in the opposite direction, toward the station, with an equal and opposite momentum as the wrench. This conserves the momentum of the person-wrench system, which was initially zero.