A 57 kg astronaut (including spacesuit and equipment), is floating at rest a distance of 9 m from the spaceship when she runs out of oxygen and fuel to power her back to the spaceship. She removes her oxygen tank (3.0 kg) and flings it away from the ship at a speed of 15 m/s relative to the ship.
At what speed relative to the ship does she recoil toward the spaceship? Express your answer to two significant figures and include the appropriate units.I tried doing (3.0 kg * 15 m/s)/(57 kg) = v_f, but it's wrong.