QUOTE (dMole @ Oct 14 2008, 06:40 PM)
Neither is it my fault that your reading mis-comprehension won't allow you to grasp my usage of "guess" and estimate from back in June of this year. Now that it is 4 months later, I have found better values for the "main" light pole mass (247 rather than 200 lbs). If one is going to go seeking an "ultra-precise" hypothetical
analysis of the light pole in question (as Smrekar appears to be seeking here) [for a hypothetical event that I don't think ever happened BTW
] then shouldn't one also
use the transverse light pole section and lamp head masses, too? Mine was after all, only an estimate from back in June there Smrekar. You seem to have forgotten that estimate
part since your post #15 on this thread BTW.
Well, seeing someone or something deleted my answer to this one, I'll just write it down again.
The mass of the light pole was in no way important as to why your calculation was incorrect. Anyone who understands the case could tell you that - but you just went ahead and calculated something impossible from it anyway, and claimed it to be factual.
Again, unless you can provide a source for your "maximum momentum limit" assertion, I'll need to assume that you do not have one. Your "'derivation" has already been showed to be severely flawed, as 5 light poles apparently did NOT stick with "perfect inelasticity" to a "B757-200" along the way to the Pentagon.
You provided it yourself.
Assuming a perfect elastic collision, the maximum possible speed of the impacted object after the collision is twice the speed of the impacting object. Therefore the maximum amount of momentum transfered can be calculated directly from this equation.
p2(max) = m2 * v2f(max) = m2 * 2 * v1 * (m1/(m1+m2))
p2(max) - maximum momentum of the impacted body after the collision
m2 - mass of the impacted body (lightpole, in our case)
m1 - mass of the impacting body (757, in our case)
v2f(max) - maximum possible speed of the impacted body after the collision
v1 - speed of the impacting body before the impact
For perfectly inelastic collision:
p2(max) = m2 * v2f(max) = m2 * v1 * (m1/(m1+m2))
Or, for any collision:
p2(max) = m2 * v2f(max) = m2 * (1 + Cr) * v1 * (m1/(m1+m2))
This is derived directly from your own source, which you claim to understand intimately. I already showed you why I'm correct with the v2f(max), and I will not do it again. The rest is just the same old equation of p = m * v.
Therefore, I believe I have adequately shown this to be correct. If not, I can write you down how you get to this, but you have to admit you don't know what to do with the provided equations first (incidentally, where did you graduate and in what field?).
By the way:
Looking at the momentum (p) in this alleged inelastic collision:
It's quite safe to assume you assumed Cr = 0, judging from your opening statement alone.
b]There is absolutely nothing wrong with that formula or your calculations[/b] (aside from using about 10 decimal spaces more than you should). It's that you made a rather preposterous assumption along the way, and drew conclusions from that."[/color]
So which is it? Or are you unable to even remember what you have already posted here Smrekar? Are there more than one of "you" perhaps?
I already answered this, but it went missing for some reason.
Your initial estimate is incorrect (to the point of being absurd). From that estimate you make a correct calculation, which gets to a wrong result. The calculation is correct - as I explicitly stated - but the initial estimate and the final result are not.
To clarify for Smrekar- I assumed that momentum would be transferred in any "collision," and that Conservation of Momentum is the proper way to analyze it. Collision physics is actually fairly fleeting and complex, despite what Smrekar has already claimed. Then I "guessed" a 1% momentum transfer in my estimate
, which actually does look excessive, 4 months
later. If we trust Smrekar's "perfectly inelastic collision" analysis, then my "guess" was 1.00/0.193 ~= 5.18 times too high for an alleged 530mph aircraft collision of unknown duration
. FYI, this was the first consideration of light pole "momentum" that I had seen anywhere by anyone, and there wasn't much information out there- had to assume
[previously discussed here] in order to proceed. BTW Smrekar, 5.18 <<
Interestingly enough, I didn't have access to any information which you didn't have, yet I was able to make the calculation, but you weren't. Quite interesting.
Where did you say you worked?
I didn't use a coefficient of of restitution in my estimate back in June. I don't think we have enough information about the "V_2f" in this case to determine that exactly, do we? If so, I'd love to look at something sourced there, Smrekar.
We do have sufficient information to determine your "conservative estimate" was approximately three times above being physically possible, and approximately five times above being plausible (seeing that coefficient of restitution will not be very high for the light pole or the plane).
So what did you obtain for the light pole base shearing force(s) then Smrekar? You appear to be alluding as much in your "light poles tend to be fixed to the ground" 4th option above. What percentage of the B757-200 momentum have you calculated there Smrekar (and how many times)?
Quite simply, I didn't. I didn't intend to calculate the speed of the light pole after the impact, nor did I pretend to have the sufficient information to do it. I only pointed out your calculation was way beyond the realm of reality.
Actually with your demonstrated inability to comprehend written matter, I'm growing quite weary of conversing with you. I actually have done another analysis that is less of a "back of the napkin" estimate, but it involves several mathematical assumptions Smrekar, so I'll spare you the details. Also, there is a more applicable collision concept to use here Smrekar, but I'll let you discover the particulars for yourself.
Go ahead, let's see what you can do