A 55 kg astronaut is in space, far from any objects that would exert a significa

Question

A 55 kg astronaut is in space, far from any objects that would exert a significant gravitational force on him. He would like to move toward his spaceship, but his jet pack is not functioning. He throws a 700 g socket wrench with a velocity of 4.7 m/s in a direction away from the ship. After 0.58 s, he throws a 870 g spanner in the same direction with a speed of 7.3 m/s. After another 8.6 s, he throws a mallet with a speed of 5.2 m/s in the same direction. The mallet has a mass of 2,500 g. How fast is the astronaut moving after he throws the mallet? [Note: All speeds are with respect to the spaceship.]

Explanation / Answer

Work out the momentum of all the thrown objects. This will equal the mans momentum. Because we know his mass we can work out his velocity, since momentum is conserved, and by throwing the things we will experience an equal but opposite force, or equal and opposite momentum. Time is irrelevant in this scenario since there is no friction to consider (in space).

p=mv (momentum=mass*velocity)
Momentum (total): .700*4.7+.870*7.3+2.500*5.2=22.641N m^-1
Momentum (man)=Momentum (total of objects)
55*v=22.641
v=22.641/55
v=0.41165
v=0.41m s^1 (1 SF)

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