Was posted in alt.machines.cnc... But doesn't seem to have migrated over
I scored a 430...
I've got the unfair advantage over some of you of being trained here on the
job... But never had schooling in most of this so...
Share your score with us... No shame or bragging rights, just a fun test.
Joe Agro, Jr.
Automatic / Pneumatic Drills: http://www.AutoDrill.com
Multiple Spindle Drills: http://www.Multi-Drill.com
: Was posted in alt.machines.cnc... But doesn't seem to have migrated over
: here yet...
: I scored a 430...
I scored a 420, and I think their answer for question 31 is wrong. I
measured from the center of gravity of the load to the fulcrum, and
they measured from the outer edge of the load to the fulcrum.
I emailed them about it, so I'll probably find out that I screwed up.
It's a fun quiz, thanks!
Right, the correct answer is 60. Not seeing that as an option, I
figured out how they measured it and chose their answer.
Also the question about naturally aspirated pistons was ambiguous.
There were two correct answers, depending on your point of view. The
retreating piston creates a lower pressure inside the cylinder, but
one could argue that both the retracting piston *and* the natural
atmospheric pressure work together to force air into the cylinder.
They marked that one wrong, but I knew I had a 50/50 chance.
I got the balloon one wrong, but I think they're wrong, or at least
ambiguous. For the baloons to be different sizes in the same air
space (as shown), they have to be of different composition, so they
all are in the "same air" and thus atmospheric pressure (PSI) is the
same (14psi at sea level, for example) but the balloons themselves
exert varying pressures on the gasses therein. Had they asked which
had the highest pressure INSIDE the balloon, I would have gotten their
answer. Unless they meant TOTAL pressure exerted by the atmosphere,
in which case they should have asked for that (and in which case, the
contents of the balloons is irrelevent). Or if they assume the
balloons have not yet reached steady state, but that wasn't mentioned
in the problem either.
Or maybe I was just over-analyzing it. The picture does show them in
common air, though. Had they drawn lines between the balloons, to
show them possibly in different air pressures, I would have gotten it
This one triped up every engineer here that has taken the test so far.
I was thinking along the same lines at first, noting that if you measure
from the center of each box to the fulcrum, the the distance ratio appears
to be 5:1 but that results in an answer of 60kg, and that ain't an option
If you look at it as each box sites on two segments, and count that way, or
in other words if each segment was shown as the width of a box, the the
ratio appears as 3:1 which provides the correct solution.
I see two triangles point down.
center of mass _is_ the same as the point of contact with the lever.
The lever is already marked in uniform segments.
The one on the left is _two_ segments out from the fulcrum
The one on the right is _six_ segments out from the fulcrum.
How in name of do you come up with anything other than 3:1??
: I see two triangles point down.
: center of mass _is_ the same as the point of contact with the lever.
: The lever is already marked in uniform segments.
: The one on the left is _two_ segments out from the fulcrum
: The one on the right is _six_ segments out from the fulcrum.
: How in name of do you come up with anything other than 3:1??
Aha! They got my message and fixed the question!
It used to be two squares, and the answer they wanted was based on the
*outer* edge of each square, not the center. I suggested that using
triangles or circles would make it easier to see where the center of
mass was; you wouldn't have to decide between the inner edge, the
center, or the outer edge.
Simple: they changed the picture between then and now, presumably in response
to numerous complaints that their answer was wrong. At the time HDRDTD and I
posted, the picture looked something like this (view in a fixed-space font):
| | | |
-- -- -- -- -- -- -- --
As illustrated, the centers of mass are at 1 unit, and 5 units, distant from
Doug Miller (alphageek at milmac dot com)
: If you look at it as each box sites on two segments, and count that way, or
: in other words if each segment was shown as the width of a box, the the
: ratio appears as 3:1 which provides the correct solution.
No, then the ratio is 2.5 : 0.5, or 5:1, because the center of one
weight is halfway through the 3rd double segment, and the center of
the other weight is halfway through the first double segment.
I think it's clearer if you use circles or triangles to represent the
weights, so it's more obvious where the weight "is".
Or, think of each side as having two weights, each one segment wide
and half the total weight. You can treat the total weight as being at
the midpoint between the two weights, but you clearly can't ignore the
position of one weight and treat the total as being at the end of the
I found this question doesn't have a correct answer. This is a simple
"moment arm" calculation. The center of gravity of the weight to the
fulcrum. In real life, the board itself must be considered, and it,
too, has a moment arm. "60kg" is correct but not a choice.
470, but I wasn't impressed by some of the questions. As an example,
the "two boxes on a seesaw" has a range of possible answers, depending
on whether they're a point mass or a distributed mass within the box.
To get their answer you have to assume a point mass, that's a pretty
tenuous stretch of the imagination. Redrawing the diagram a little
better would clarify things.
Anyone found the full set of correct answers yet? I'm too busy just at
the minute, but it would be interesting to see them.
When you can see the results, it's easier...
Q7 (which geartrain is which) is just plain wrong. Even allowing for
crazy Yankee terminology, there's no way that the one train of three
pinions (the others are all 2) can be "reverse". That's not mechanical
aptitude, that's assuming that you're looking inside a RWD car gearbox
(where the extra idler gear is indeed used for reverse) -- but then
"direct drive" in that context wouldn't be using any of the gears.
Q45 The balloons are another bad question. Three balloons illustrated
as being next to each other? Of course the atmospheric pressure is
identical (Pascal's principle, if you care), it's far more likely that
they're made of thicker rubber than there's some sort of barometric
change across the page.
I missed the one regarding the normally aspirated engine. I thought
long and hard about it because I considered it ambiguous. I know this
has been discussed here but this is my take:
The airflow is not caused just by atmospheric pressure alone, nor by
the vacuum created within the cylinder alone. It's the differential
in pressure which causes the airflow. So, to me, although neither of
those two choices were precise, it had to be one or the other. I
guessed wrong :-)
For that matter, you could even say it's caused by gravity since
without gravity there would be no atmosphere nor atmospheric
pressure :-) So the answer should really be (a)(b) and (c)
The other one I missed was the one with the various drive train
components. I knew which way all the gears were spinning but had
trouble with the terminology of the labeling.
On 24 Oct 2007 17:56:40 -0700, firstname.lastname@example.org wrote:
Agree! And, that makes the test (or at least that question) invalid
for measuring aptitude. Perhaps it would be valid as an exit exam
after a course of instruction in which terminology/jargon was defined,
but not as an entrance exam prior to exposure to the jargon.
(I missed that one, too. So maybe the above is just a little sourness
in the grapes.)
If you look back now, you'll see that they've changed the seesaw
question in the test! Maybe the authors are reading this newsgroup?
OTOH, the change they've made (triangular boxes) is farcical and shows
that they really don't understand the issue that was raised 8-(
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