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Author Topic: Puzzled?  (Read 4689 times)

Offline Equalizzer

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Puzzled?
« on: 13/11/2005 19:34:55 »
Your in a falling lift, if you jump before it hits the bottom, so your i nthe air when it stops.
would hurt you at all?
would you be able to jump?
would the impact break your legs?


this has puzzled me


thx[?]



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mix, H2O and H2O and you get, well, just H2O. =p


 

Offline neilep

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Re: Puzzled?
« Reply #1 on: 13/11/2005 20:14:21 »
I suppose it depends on a number of things...like how fast is the lift plummeting ?...how tall is the lift ? and how high can you jump ?...but I happen to know how ever hard you jump ...YES, you will most probably not just break your legs but your spine and neck and all the nice crunchy things that like to snap on impact, as well as a few internal organs too....

Unless, you can jump so that you cancel the speed of descent...and then...you'll probably just jump through the roof of the lift...which isn't nice and will most certainly ruin your day.

But lets hope a passing ' plummeting lift ' expert passes by and comments

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another_someone

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Re: Puzzled?
« Reply #2 on: 14/11/2005 01:55:13 »
My two pence worth.

If you jump up from a surface, you are jumping up relative to that surface, and will land back (allowing for losses due to air resistance, etc.) with the same speed you kicked off with, but in the opposite direction – i.e. The harder you kick off, the harder you land.  You now have to add this onto the downward speed of the lift at the point of time you lift off from the lift (that is you frame of reference).

Thus, if at the point that your feet leave the floor of the lift, you were travelling upward at 15mph (just a random number), then (ignoring losses due to air resistance) you will land back on the floor with a downward velocity of 15mph.

If the lift was falling at a rate of 200 mph at the time you launched, then you will lift off at a nett speed of 185mph downwards, and land at a speed of 215 mph.  If the lift is continuing to move downward at 200 mph, then your collision speed will be 15 mph downward; but if the lift has stopped because it has hit the ground, then your collision speed will be the full 215 mph (i.e. You may have delayed the impact, but when it happens, it will be worse).

No, I am not a plummeting lift expert, so the above is guesswork, but it is what I would expect from my naïve knowledge of such things.

 

Offline ukmicky

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Re: Puzzled?
« Reply #3 on: 14/11/2005 04:59:28 »
1.You would have to know exactly when the lift was going to hit the ground.

2.You would have to jump at the same speed as the lift was falling (watch your head mate)

3.You wouldnt be able to jump because you would be in freefall,as the lift was falling you would be floating in the air, just like them astronauts doing  weightless training in one of them planes that dive to simulate a weightless enviroment.

:)



Michael                                      
« Last Edit: 14/11/2005 05:00:07 by ukmicky »
 

another_someone

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Re: Puzzled?
« Reply #4 on: 14/11/2005 07:05:47 »
quote:
Originally posted by ukmicky

1.You would have to know exactly when the lift was going to hit the ground.

2.You would have to jump at the same speed as the lift was falling (watch your head mate)

3.You wouldnt be able to jump because you would be in freefall,as the lift was falling you would be floating in the air, just like them astronauts doing  weightless training in one of them planes that dive to simulate a weightless enviroment.

:)
Michael                                      



Number 3 is not an issue.

Firstly, I suspect the frictional effects of the runners would prevent true free fall.

Secondly, even if you were in true free fall, it would not stop you from jumping up, it would simply stop you from coming down again (at least until you bounced off the ceiling).

Thinking about my earlier answer, I would make a change to it.

I had not made allowance for the fact that effectively, when the lift hits the ground, the lift floor will in effect be coming up to meet you mid air, so you wont be doing the full round trip – but this assumes it catches you before you have started the descent – in fact, before you have even reached the apex of your ballistic flight, at which point your speed will be zero with respect to the list floor at the time you left it, and so you will from that point on gain no advantage.

On the other hand, if you are to lift off from the floor of the lift with a speed equal to the downward speed of the lift, then the G forces on your body at lift off will be exactly the same as the G forces that you will experience when the lift hits the ground – so there is no advantage there.
« Last Edit: 14/11/2005 07:51:56 by another_someone »
 

Offline ukmicky

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Re: Puzzled?
« Reply #5 on: 14/11/2005 12:43:35 »
The increased mass of the lift due to its momentum would quickly negate any braking effects through banging on to the sides of the runners, and once in freefall it would be very hard to keep your feet underneath you:)

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Offline neilep

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Re: Puzzled?
« Reply #6 on: 14/11/2005 13:06:28 »
Don't forget to get out at the SPA (usually the last stop) for a quick massage before returning to the lift for the remainder of your pleasant journey.

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Offline Thondar

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Re: Puzzled?
« Reply #7 on: 14/11/2005 21:49:32 »
I'll go for....The Cracking Legs Sound!

I mean, the acceleration must be something right (gravity) so, how much force you would have to use to compensate that.

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Offline ukmicky

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Re: Puzzled?
« Reply #8 on: 14/11/2005 23:26:38 »
i saw a picture of a man who jumped from a skyscraper,there was nothing that resembled a human left.it looked like 200lbs of mince meat.

Michael                                      
« Last Edit: 14/11/2005 23:27:17 by ukmicky »
 

Offline jezza

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Re: Puzzled?
« Reply #9 on: 16/11/2005 13:48:23 »
well, i dont think you would be able to jump at all if you think about it, its hard to imagine, but if you picture your self in a lift plumiting at 200mph, i dont think you would be able to jup, it would feel like there is a huge weight on top of you.

well thats just what i think, there no scientific backing for it.
 

Offline jezza

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Re: Puzzled?
« Reply #10 on: 16/11/2005 13:58:51 »
i just read this

If the elevator fell 12 storeys, it would be going about 95 kilometres an hour at impact—and so would you. Any jump you made might delay the inevitable for a fraction of a second but would have no effect on the final outcome—which would not be pretty. If your timing was absolutely perfect and you jumped exactly when the elevator hit, you might reduce your speed at impact by a negligible eight kilometres an hour
 

Offline rakarthxii

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Re: Puzzled?
« Reply #11 on: 17/11/2005 22:37:55 »
Considering the problem in a slightly different way shows that there no chance of survival.

Rather than an elevator, our (soon to be a corpse) man is standing on a simple concrete slab falling down the corridor where the lift would normally be.

The terminal velocity of our man is about 45m/s and his weight is about 75kg

Say the man, seeing his impending doom, attempts to jump for his survival. For a normal jump, I'd guess the man to have velocity=0.75ms

So... the momentum of the man going downwards
is 45*75 =3375 Newton seconds.

the momentum of the man jumping upwards
is 0.75*75 =56.25 Newton seconds.

Overall momentum + 3375-56.25 =3318.75

All that momentum is going down, the mans overall speed has only decreased by 0.75m/s - he is going splat [xx(]

The whole idea is like throwing a football at a speeding train and hoping that it will stop.

If you want experimental proof - think back to the last time you went on a roller-coster. imagine trying to jump against the force you feel when dropping.
 

Offline ukmicky

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Re: Puzzled?
« Reply #12 on: 17/11/2005 23:24:22 »
True story
when i was a kid i went on an old fashion type rollercoaster in margate, the type without the over the shoulder type restraints.
As it went over a bump i came out of my seat and ended up in the lap of the person sitting behind me.
It took me twenty or so years to get over it, and the only reason was because i went back to the same place with my kids and some of their friends who wanted to get back on the same ride, it was still there.

I didnt want my kids friends to tell them there dad was a sissy:)




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« Last Edit: 17/11/2005 23:25:04 by ukmicky »
 

Offline DoctorBeaver

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Re: Puzzled?
« Reply #13 on: 18/11/2005 16:22:37 »
ratharxii - you forgot to allow for the fact that as the man jumps, the  force of his jump would accelerate the slab slightly & reduce his upward momentum accordingly (equal & opposite reactions, and all that)
 

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Re: Puzzled?
« Reply #13 on: 18/11/2005 16:22:37 »

 

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