A 83.5 kg astronaut is working on the engines of a spaceship that is drifting through

space with a constant velocity. The astronaut
turns away to look at Earth and several seconds later is 35.5 m behind the ship, at rest
relative to the spaceship. The only way to return to the ship without a thruster is to throw
a wrench directly away from the ship. The wrench has a mass of 0.599 kg, and the astronaut throws the wrench with a speed of 21.6
m/s.
How long does it take the astronaut to reach
the ship?
Answer in units of s

1 answer

Calculate his speed going back to the spacecraft after throwing the wrench, using conservation of momentum.
Then divide 35.5 m by that speed.