Exam question assistance please

He did. That was in fact the whole point of the question!
Well don't say I didn't try to give you a hint. The spars consist of triangles, all facing the same way and with their bases touching each other. To find the total area of metal in the triangles in each of the three cases. Area of each triangle = 1/2 base x height. As the bases touch then the sum of the base length is the length of the beam - in all three cases. The height is the depth of the beam - in all three cases. Therefore the total area of metal = 50% of the cross sectional area of the beam - in all three cases.
It doesn't matter what shape the triangles are in such an arrangement. The area will always be half that of the beam. The triangles can even be non symmetrical without affecting the solution and in fact it still doesn't matter if they aren't all the same shape.
Reply to
Dave Baker
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I am flabbergasted.
I am applying for a job as a Trainee Locomotive Driver, and this is one of the Sample Test questions sent to applicants to familiarize them with the entrance examination. (This by the company that runs the rail system in this state)
If Engineers can't understand the question, what hope have hope-fulls like me got?
Another question that would have to fall into the category of "Very Poorly Written" surely:-
The question is, "Which gate is the strongest?"
It is at:-
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I would suggest that both gates B. and C. are identical in strength, as they are identical in construction, only the method of mounting is different. However, that is not what the question is in my view.
Another point is that a gate is presumed to be for the purpose of keeping something in or out. This being the case, the direction of force requiring strength would be presumed, in the absence of contra-indication in the question, to be parallel to the ground and at right angle to the face of the gate. This would also result in A. & B. being equal in strength would it not?
I would suggest that the question, based on the given answer, should have read "Which gate is mounted in the strongest way?"
The answer sheet providing their logic is at:- [Question (8)] You will need to click on LARGE at mediafire:-
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It also gives their logic to the girder question (8)
Reply to
Phill
Phil,
I can't respond to your particular points since I can't raise the image on the web site, but one major force present in a gate is its own weight. In a long gate, like a farm gate, the moment of the weight about the hinges can be significant. So I believe that the preferred way of building a gate is to place the diagonal struts(s) so that it(they) are in compression rather than tension under the force of the weight.
Jim.
Reply to
Jim Guthrie
Oh sh*t! Now this is really stupid. The question wasn't asked well (leaving out constraints) and the construction shown wasn't very clever (none of the three) and then they ask that a loco driver? I bet they didn't give an explanation why a) might be the solution.
Try to make the pilot's exam, their questions should be more logical. :-)
Nick
Reply to
Nick Mueller
You would have to hope so....:-)
Reply to
Phill
It's related to the second moment of area, no?
-- Nige Danton
Reply to
Nige Danton
And Barnes Wallis and the Wellington Bomber! Or for the really wheelies-- the bird cage construction on cars.
Mark is usually right-- cornflake packets or
A HOUSE OF CARDS!
Well?
Reply to
ravensworth2674
Still am convinced of my answer*). But that question is quite stupid, because girders don't look that way. If the triangles weren't solid (but tubes) it wouldn't be a girder but a structural frame**). And then, a) would be right.
*
) with one assumption on how it is supported. Can argue in detail if you want.
**) Looking in the dictionary, I see that a structural bridge is called "girder bridge". I thought that "girder" is an I-beam. Don't you distinguish between the two or is my dictionary wrong?
Nick
Reply to
Nick Mueller
I think they are using the term as a structural element, it can also be a structure in itself though.
Reply to
Phill
So girder can be an I-beam, but also be something more general? To be more specific, is "structural girder" a valid expression? And an I-beam zigzag-cut/shifted/re-welded is called a honeycomb beam/girder?
Nick
Reply to
Nick Mueller
...Of course there was the one about the Irish labourer that was asked the difference between joist and girder...he said "Joist wrote Ulysses and Grider wrote Faust"...
Regards, Tony
Reply to
Tony Jeffree
I'm not counting them as complete triangles
because top and bottom you got beams ...
this is supposed to be a girder ...not a bunch of triangle sections stitched together
I'm counting them as diagonal spars ...
on "c" you have 14 diagonal spars
on "a" you have 8 diagonal spars.
the top and bottom of the triangles is already there in both cases as the beams ...
so you got two girders to compare
one with 8 spars ... and one with 14 spars . welded to the top and bottom beams .
thats how i see it .
all the best.mark
Reply to
mark
The triangles were solid. Question during the test: "Sir, are these triangles *really* solids?" And if the answer is "Yes!", try to look as stupid as possible. :-)
Nick
Reply to
Nick Mueller
I thinks thats it exactly. Isn't it bd squared over 12 or something like that?
Peter
Reply to
Peter Neill
In article , Nick Mueller >So girder can be an I-beam, but also be something more general?
I was taught "castellated beam/I-beam/RSJ".
Regards,
David P.
Reply to
David Powell
Depends on how the gate is made. An old fashioned 5 bar all timber gate with dowelled, morticed & tenonned corner joints would have a compression brace - no need to tie the brace to the frame corners. A welded metal gate frame would have a thin tension brace welded at the corners.
Ledgered and braced sh*t-house doors are often hung upside down, the braces should be in compression, transferring the load to the ledgers. If you have one hung wrong, with a corner dragging on the floor, the easy fix is a tension brace - a loop of steel wire between top hinge side and bottom lock side, fixed by two bolts, then tighten using spanish windlass method and secure.
Regards,
David P.
Reply to
David Powell
In article , Richard >>
Sadly this sort of test question is becoming all to common. Acceptable in a Sunday night pub fun-quiz for a prize of a few pints of beer, but not if the test is to relevant to employment, etc. I've seen some horrors in the amateur radio test questions, electricians' trade test stuff and even in the driving licence written test. Intentionally, no comment on recent A-level maths and science papers, it would be very bad for my blood pressure.
Regards,
David P. C.Eng, MIEE (or whatever the IEE calls itself now.)
Reply to
David Powell
Well if you don't want to answer the question that was actually set there's probably little left to discuss.
Reply to
Dave Baker
Clearly B is the strongest. A has no diagonal bracing at all and C has the brace running in the wrong direction.
Reply to
Dave Baker
its another stupid question, strength depends on what use the gate is put to ..
but as a farm gate ...
C is how most of them are made ....and would be the answer examiner is looking for .
C is least likely to buckle or sag when someone swings on the end of it
and is economical compromise over metal used.
on c the brace acts like suspension bridge
where as A would survive a charging rhino, full on, into it.better than C...it has not the same abilities to survive someone swinging on it...or the test of time over sag.
B is just bad design with brace running wrong way.
no rhinos in the uk .....so C is best.
all the best.mark
Reply to
mark

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