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A 747 nose dives into the atlantic ocean and hits the water at 900 km/h

  1. Mar 8, 2008 #1
    Roughly estimate the maximum deceleration of the aircraft parts.
     
  2. jcsd
  3. Mar 8, 2008 #2
    this seems to be a homework problem, however for a rough estimate you should look at the force the water would exert on the area of the plane, however for that you would have to estimate the area of the plane.
     
  4. Mar 8, 2008 #3

    Danger

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    Yeah, not nearly enough information provided for an informed estimate. First off, no pilot with any modicum of control would go nose-first into the water. A high-engine job like a DC9 can skip like a flat stone during a belly-landing ditch. Something with honkin' huge high-bypass turbofans slung under the wings would come to a very rapid and uncomfortable stop, and not in one piece. The surface conditions and even temperature of the water make a tremendous difference as well.
    If this is a homework problem, you should point out to your teacher that the question is very badly worded.
     
  5. Mar 8, 2008 #4
    It is not a homework problem and it is not badly worded at all. Also, The problem is pretty much well defined, because we can all look up the properties of a 747 and we know what water is.

    This sort of problem is like what you kind find in the book "Problems in Physics" by the famous physicist P.L. Kapitza. E.g. try solving this problem which is taken literally from his book:

    "A stone falls into the water and water drops are splashed. Why do the water drops fly upwards? Does the maximal height reached by the drops depend (primarily) on the size of the stone or on its speed? What is the maximal height?"
     
  6. Mar 8, 2008 #5

    Danger

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    Alright, I admit that I had forgotten the title of the thread when I first responded, and you didn't mention the type of aircraft in the post, so I took the broad-spectrum approach.
    You do realize, however, that not all 747's use the same engines... right? You also did not specify whether the gear was up or down, what flap angle, leading-edge flap angle, aileron deflection, elevator deflection, and spoiler deployment were in place, nor the weight of the bird at impact. How many passengers of how much weight and weight distribution? How much cargo to the nearest tonne or so? Fuel tanks full, empty, or somewhere in between? Is your 900 kph airspeed or groundspeed? How high are the waves and how fast are they moving? Why specify the Atlantic Ocean as opposed to any other body of water when you didn't even mention what model/year of 747 it is?
    Tell me again that it wasn't badly worded.
     
  7. Mar 8, 2008 #6
    These sorts of problems are made to let one think about the relevant factors. If you very precisely give all the information you can give away hints on how to solve the problem. That's why I said: "roughtly estimate". It is not a textbook "homework problem". And, of course, you can then just make certain simplifying assumptions about the factors you mention.
     
  8. Mar 8, 2008 #7
    It's not badly worded, but there is not nearly enough information there. Why don't you do look up the information or the properties!!
     
  9. Mar 8, 2008 #8

    Danger

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    I'm a pilot. We don't make 'simplifying assumptions'. When lives are on the line, you have to know exactly what you're getting into.

    edit: I just realized that being a bird-driver might have coloured my response, and I came off as being overly antagonistic (more correctly, territorial). My apologies for that. Most ground-hogs can't understand just how much of a personal relationship is involved between a bird and its driver. You don't fly an aeroplane; you wear it. As soon as you strap it on, it becomes part of your body. I let my emotions get in the way of a proper response. Again, my apologies.
     
    Last edited: Mar 8, 2008
  10. Mar 21, 2008 #9
    About the book by Kapitza

    Hi I have been solving problems from some Russian books e.g. 'Problems in general Physics' by I.E. Irodov and by S.S. Krotov....the problems in these books are very interesting...I want to know more about the book by Kapitza...its Publisher of english translation its cost etc..can you please help me out for that. thanks E-Mail saurabhid@yahoo.com
     
    Last edited: Mar 21, 2008
  11. Mar 21, 2008 #10
    The problem here is that we are being asked what the maximum deceleration is. You could make a reasonable guess at the average deceleration, but the maximum deceleration could be a 100x as big for a small part that breaks off.
     
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