A 60 kg astronaut floating in space outside the capsule throws his half kg hammer such that it moves with a speed of 10m/s relative to the capsule. What happens to the astronaut?
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When the astronaut throws the hammer in space, an opposite reaction occurs according to Newton's third law of motion. The astronaut will experience a force pushing them in the opposite direction to the hammer's motion. This force is equal in magnitude but opposite in direction to the force exerted on the hammer, resulting in a net force of zero on the system of astronaut-hammer.
Due to the conservation of momentum, the total momentum of the system (astronaut + hammer) before the throw is equal to the total momentum after the throw. Since the astronaut and hammer were initially at rest relative to each other, the total momentum before is zero. After the throw, the momentum of the astronaut and the hammer cancel each other out, resulting in a net momentum of zero.
However, the astronaut experiences a change in position. Since the momentum of the hammer is in the opposite direction to the initial position of the astronaut, throwing the hammer propels the astronaut in the opposite direction. This is similar to how a person on a skateboard moves backward when they throw something forward.
Therefore, after throwing the hammer, the 60 kg astronaut will start to move in the opposite direction of the hammer's throw with a certain velocity, but the total momentum of the system remains the same.