I really don’t know. I’m guessing that if the elevator was falling at a high speed, which it most likely would, jumping might almost be impossible. I could be totally wrong, but even if it wasn’t a matter of gravity effect, timing a good jump and using the strength to do so in what is likely three seconds would be pretty damn hard to do. And even if you managed to jump right before the impact, (which you’d have to know 100%) I’m not sure how much that would really minimize the injury.