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Discussion on META:

Questions related to geopolitical events

Suppose you have an office tower, weighing around 300,000 metric tons, and has a height of 200 meters.

It support structure is made of iron and steel, which both melt around 1500°C.

I believe iron melts at a pressure of 225Gpa, at least at the core of the earth. I was unable to find a similar estimate for steel, but I presume it is greater than that of iron, so suggest that pressure be used (225Gpa).

The building collapses at free-fall for around 10 seconds, so friction is nil.

  1. Can the free-fall of the building generate and transfer enough energy to the metals to melt them?

  2. If so, at the moment of collapse what temperature would the respective metals have to be for the event of collapse to melt the iron or steel?

EDIT

I am making this edit to remove any implication that this question is "homework" (i.e. ”[a] question whose value lies in helping you understand the method by which the question can be solved, rather than getting the answer itself.”).

The foremost reason this question is not homework is that I've no real interest in the method, only the conclusion. Any method of reaching the conclusion will do fine.

However, I'd run some thoughts on a napkin, so to speak, which will also help allay any concern about the possibility of "homework".

The workings I had contemplated were along the lines of:

Iron melts under 225Gpa = 2.25e+11 Pa (2.25 x 1011) = 2.25e+11 kg/m2. The building fell without resistance accelerating at 9.8m/s2. For simplicity let's suppose the top of the building weighed 3e9 kg. 2.25e+11 kg/m2 / 9.8m/s2 ~= 2.29e10 kg.

This is laughably rough, but I figured it'd be a useful baseline for eliminating the possibility. Based on my napkin, to melt iron, I'd expect that the top of the building would've had to have weighed an order of magnitude more than it does, plus a host of other assumptions.

But of course, as you've probably gleaned, the assumptions are broad and I'm oversimplifying and/or quite possibly confused about the relationships between the laws and facts. For example, I do not take into account the the spread and uniformity of application of the energy, nor speed of dissipation of heat (over the 10 seconds of the fall), so I figure something's missing, or there's just a much better method of arriving at the correct conclusion.

Hence I posted this question. I hope this alleviates any concern about whether this is "homework" (and in any case, I noted "As a general rule, we do not discourage homework questions")

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closed as off-topic by CuriousOne, John Duffield, Bill N, ACuriousMind, Gert Dec 21 '15 at 23:22

  • This question does not appear to be about physics within the scope defined in the help center.
If this question can be reworded to fit the rules in the help center, please edit the question.

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    $\begingroup$ I'm voting to close this question because it's not a genuine enquiry, and is instead a vehicle for linking to WTC "controlled explosion" conspiracy theory. $\endgroup$ – John Duffield Dec 21 '15 at 22:11
  • $\begingroup$ Incidentally, steel does not melt at 2700 C - more like 2700 F. 2700 C is really very, very hot - very few metals remain solid up there (I think only osmium, rhenium, tantalum and tungsten, see this link). $\endgroup$ – Floris Dec 21 '15 at 22:17
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    $\begingroup$ Even if this shouldn't be classified as a homework-like question (and I'm not sure whether the edit you made changes that), I don't think it's on topic because it still just seems like you're asking us to do a calculation for you. $\endgroup$ – David Z Dec 22 '15 at 17:35
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    $\begingroup$ @DavidZ As you undoubtedly saw from the answers you deleted, there are a variety of concepts that can be employed to answer the question. Which applies to answer the question is as useful as the calculation itself (to me, at least). $\endgroup$ – Brian M. Hunt Dec 22 '15 at 20:13
  • $\begingroup$ I agree with @DavidZ $\endgroup$ – Little Bowsette Jan 31 at 16:13