I don’t think you can jump off something that is falling because you’d be falling with it. Think how you would jump normally: you start with bending your knees so then when you unbend them you push against the floor. But if the floor and yourself are both in free fall, when you bend your knees there’s nothing to make you stick to the floor, so your torso won’t go down, instead your feet will go up. So then you can’t push against the floor.
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