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? for physics minded people

Discussion in 'Off Topic Threads' started by kiwiG, Sep 26, 2010.

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  1. kiwiG

    kiwiG Member

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    Hi Guys, Conversation found it's way to stories of survival against the odds...specifically...the guys who fell out of crippled bombers at 40,000 feet during WWII and survived the fall. Not being physics minded, the next question was...how long would it take to reach the ground? Any help appreciated. Thanks-Graham.
     
  2. hmb

    hmb Well-Known Member

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    About 3 minutes and 45 seconds. HMB
     
  3. BFJ201

    BFJ201 TS Member

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    2nd for what HMB said. I actually came up with 3:48.5 but it all depends on what you use for your terminal velocity of a falling human. I used 54 m/s (120.79 mph). One would reach V(t) in 5.51s while covering a distance of 488 ft. The skydiver would then take 223s (3:43) to cover the remaining 39,512 ft. Giving a total of 228.5s or 3 min 48.5s

    James Allen
     
  4. quartering

    quartering Active Member

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    how high did they bounce?
     
  5. JerryP

    JerryP Active Member

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    curious, I checked out the ceiling height of the bombers.

    B-17: 35,000 ft.

    B-29: 40,000
     
  6. Quack Shot

    Quack Shot Active Member

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    How do you calculate the wind resistance and the effects of someone screaming at the top of their lungs in a reverse direction. Also the possibility of liquid propulsion from the other end.
     
  7. Chango2

    Chango2 Active Member

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    Outside Magazine recently had an article about some guy who plans to skydive from 120,000 feet. That's right, 120,000 feet. All kinds of danger/technical problems etc. Prior record was 105 thousand feet. Anybody know the status of this? In part done to help develop escape mechanisms for the space shuttle etc. Was quite an interesting article, among other things, the human body has problems when exposed to sonic speeds...big time problems, like shearing apart. Other problems include velocities that can rip a spinning human's head from the brain stem. Scary serious stuff to test out.
     
  8. recurvyarcher

    recurvyarcher Well-Known Member

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    If they are airborne, then they've been taught how to fall before pulling the chute. So if they keep their wits about them, they have a *slight* chance of surviving. My son (82nd airborne) taught his brother and me, because we sky dive (past tense for me).

    If you've ever been skydiving, you know the arch position, facing the ground. That person will fall more slowly than a person who is falling feet or head first. But you want to land feet first, with your knees slightly bent. Cover your head with your arms all the way through the bounce.

    Of course, you have a much better chance of survival if you land in deep water, dunes, or really thick vegetation (if you can keep from getting impaled), or if you can manage to fall on somewhat of an incline so your momentum is not upbruptly stopped. A good skydiving instructor will tell you how to steer your body in the air, so I imagine that they get that kind of instruction in the service, too.
     
  9. ricks1

    ricks1 TS Member

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    I bet the bomber was shot down by a trap shooter and the 29yd line
     
  10. phirel

    phirel TS Member

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    I calculated 3 min and 48 seconds if the person, or anything else were falling without air resistance and if gravity was constant from 40,000 ft to the earth surface (it is not). If you add air resistance to the question, it becomes much more complicated than I can deal with.

    Pat Ireland
     
  11. School Teacher

    School Teacher Well-Known Member

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    I remember a news account and in person interview of a stewardess of some European airline who survived a fall from altitude (20,000 feet or so) by landing on the snow covered slope of a mountain and having the mountain's slope decelerate her fall so that she was not killed. The interview was conducted from a hospital bed but she was in good condition without major injuries. Everyone else on the airliner was killed.

    I also remember from military training back in the 1960's that a free falling person reaches a velocity of around 110 miles per hour so that if a pilot ejects from an aircraft in a high speed dive, the pilot will actually be slowed to the 110 mph terminal velocity, given that the aircraft was at sufficient height for air resistance to slow the pilot down to the terminal velocity limit.

    Ed Ward
     
  12. kiwiG

    kiwiG Member

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    Thanks all. The incident I could recall reading about was a guy got shot out of a British Lancaster bomber...I could not recall the exact altitude...he was unconscious for most of the descent, and woke up at the bottom of a stand of tall trees...apparently he must have flopped down through them like a rag-doll bleeding speed all the way...both his legs were broken however...still a helluva lot betteroff than dead. Thanks again-Graham.
     
  13. Bisi

    Bisi TS Member

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    Recury, you surprise me. All of your posts on this site indicate an intelligent person wrote them, but then today you posted that you have jumped out of perfectly good airplanes. WTH is up with that?
     
  14. Chango2

    Chango2 Active Member

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    I bet skydiving is safer than some motorcycling activities..like Baja racing.

    But this brings to mind: The fascinating story/saga of D.B. Cooper, remember him? Did he survive? Why wasn't lots of $$ and/or a corpse found?


    This may have been a good post for trolling, come to think of it, but it is 105-106 outside and inside is more interesting today!
     
  15. ryanhammer

    ryanhammer TS Member

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    ^^^They did find a lot of money, in 1986, I believe. It was all serial numbered the same as the list that the fbi had, when they gave it to him. RH
     
  16. Bisi

    Bisi TS Member

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    Don't tell anybody but I heard DB Cooper was a trapshooter. All that ransom money will never be found. It was shot through the end of a shotgun, really didn't take that long either, just a couple of years.

    Last I heard was that he was working hotel/casino maintenance, and working as a lounge act 3 nights a week in Winnemucca, Nevada.
     
  17. tachyon

    tachyon Member

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    Pat, I have to disagree with your calculations. Without air resistance: d= 40,000 ft, the acceleration due to gravity is 32 ft/s^2 and the equation is d =1/2 a t^2 (assuming no initial velocity). Solving for t I get 50 seconds with an impact velocity of 1600 ft/s or 1090 mph. Terminal for sure.

    On a second note going up 40,000 ft does not change the acceleration due to gravity in any significant way. The radius of the earth is 20,925,525 ft or so. Adding another 40,000 ft only changes the acceleration due to gravity by less than .1%. Even going to the height of a satellite at 230 miles above the earth only changes the acceleration due to gravity by 10%.

    I agree with HMB and BFJ201. Free fall with increasing air resistance until the air resistance balances the force of gravity. Constant speed fall after that. You hit the ground at about 100-120 mph. Survival is rare.

    I have a number of the original papers from Project Excelsior and HALO and some papers from a German experiment during WW2 to jump from airplanes without parachutes (not very successful). I will post some of the more interesting info when I get a chance. I know that at 40,000 ft the lack of oxygen and the tendency to spin out of control was a significant problem.
     
  18. recurvyarcher

    recurvyarcher Well-Known Member

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    Bisi, that was when I was younger. Today I get frightened by things as simple as a soccer mom in a voting booth.
     
  19. tachyon

    tachyon Member

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    "Terminal Velocity Impacts Into Snow" R.G. Snyder Journal of Military Medicine 131, 1966

    "During one of the battalion drops from 1200 ft on a clear relatively warm day, an observer noted what appeared to be an unsupported bundle falling from one of the C-119 airplanes; no chute deployed from the object. The impact looked like a mortar round exploding in the snow. When the aidmen reached the spot they found a young paratrooper flat on his back at the bottom of a 3 1/2 foot crater in the snow, which consisted of alternating layers of soft snow and frozen crusts. He could talk. His only injuries were an incomplete fracture of a clavicle, a chip fracture of L-s and a few bruises. He was released from the hospital in time to return south with his unit.

    On 23 March 1944, Flight Sergeant Nicholas Alkemade an RAF rear gunner had his bomber set on fire by a German night fighter on a raid over Hamburg. He was not able to reach his parachute, stowed forward in the flaming fuselage. Deciding that jumping was better than burning he jumped at an altitude estimated at 18,000 ft. Falling at a terminal velocity of 120 mph he struck the snowy branches of a pine tree and then landed in a snow bank. His only reported injuries consisted of scratches and bruises and burns received prior to the jump. "
     
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