Online Mechanical Aptitude test

[masraum]

Originally Posted by Aerkuld

Another question that's odd is the penultimate question about the air entering the cylinder. I don't see the difference between the downward motion of the piston sucking air in and the atmospheric pressure pushing air in. For example, if the cylinder was sitting there and not moving no air would enter the cylinder. Surely the real answer is the air enters the cylinder due to the pressure differential created by the piston moving down and lowering the pressure in the cylinder below atmospheric. So isn't either answer technically correct?

My first reaction was to think, sucking!! But When I thought about it for a second it seemed that it had to be air pressure. I don't feel qualified to provide an argument.

[TerryBPP]

I bailed after 20 questions. ADD kicked in.

Its funny how little I recall from physics, mechanics & statics. I never use them in my daily grind.

[Tishabet]

Originally Posted by Aerkuld

Another question that's odd is the penultimate question about the air entering the cylinder. I don't see the difference between the downward motion of the piston sucking air in and the atmospheric pressure pushing air in. For example, if the cylinder was sitting there and not moving no air would enter the cylinder. Surely the real answer is the air enters the cylinder due to the pressure differential created by the piston moving down and lowering the pressure in the cylinder below atmospheric. So isn't either answer technically correct?

I had the exact same thought...

I scored an 88% FWIW. Better than I thought I would do considering all of the gear questions; spacial reasoning is not my thing!

[motion]

24... I guess I'll leave the tech stuff to you guys. Thank God for Pelican!

[sammyg2]

Physics majors would tell us that there is no such thing as "sucking", the piston creates a pressure lower than atmospheric in the cylinder and the atmospheric pressure forces the air into the cylinder to equalize the pressure.

[Tim Hancock]

88, The fan question is bogus as is the wording of the friction question. I must however admit to my stupidity on two of the pulley questions and my ignorance about the 2 battery questions (12v vs 24v). I don't feel bad about the battery question as I always avoid electronics when able, but I have no excuse for the simple pulley questions.

[island911]

Originally Posted by sammyg2

Physics majors would tell us that there is no such thing as "sucking"....

yeah, they are a bit sensitive to the word. ...usually used as my physics class Sucks!.

seriously, that Q sucked as well. My first thought was 'sucking is just the creation of a pressure differential' . . .my second thought, 'what if the engine is supercharged?' ..third thought, 'well I should just check the box of what I think that they think the answer is.'

[TheMentat]

The only one I got wrong was that stupid fan question... I'm crediting myself with 100%

[Mule]

Originally Posted by masraum

My first reaction was to think, sucking!! But When I thought about it for a second it seemed that it had to be air pressure. I don't feel qualified to provide an argument.

Dude, I had an argument about this with a real genius (who claimed to have built racing engines) about this very topic on the 928 board. He claimed the air "runs in." I said cool. I'll save money on a turbo & just get faster air. Here is the simple explanation. Picture a column of air to the top of the atmosphere. The air at the bottom is under the weight of the column. If it were not for this pressure, when the valve opens & the piston retreats, there would just be a vacuum in the cylinder. The atmospheric pressure of the air is what causes the air to fill the vacuum.

[sammyg2]

Most physics types don't like the word vacuum either. They're pretty funny about that stuff, maybe they should have gone to more parties in high school

[Aerkuld]

I have to admit that I had to think about the pulley questions, but came to the conclusion that you divide the mass by the number of pulleys, so 250kg divided by one becomes 250kg.

I find that a lot of test questions are quite badly written. You end up trying to figure out what the person was trying to ask and what answer they were looking for. If people are going to write quizzes they need to make sure the questions and answers are entirely unambiguous. It really doesn't take much effort to add an arrow 'A', 'B' & 'C' for example.

One of my favorite examples came a music teacher in high school. If I recall correctly the question was something like "Chopin's heart is in Warsaw but he is buried in Paris. Why?" and the students answer...

Because he was dead!

[Danny_Ocean]

Originally Posted by lendaddy

86, but that's not really an aptitude test as specific knowledge of electrical symbols, hydrodynamics, etc..is required to correctly answer several questions.

Yes I bombed the electrical questions

Hmmm...I bombed the "guess the weight" questions (pulleys), but aced the electrical.

[911Rob]

Originally Posted by TerryBPP

I bailed after 20 questions. ADD kicked in.

Ha, this one made me laugh!!!
I've got a partner in one of my businesses that tells everyone that he's got ADD, but really he's just a high paid lazy bugger that's a good example of how C students hire A students. Gets me to do all the work, all the time.

I'll try this soon and test my Construction Engineering know-how?

More answers first though please........ I cheated alot in college.

[Flatbutt1]

72 which is why I write checks.

[masraum]

Originally Posted by island911

'what if the engine is supercharged?'

IIRC, the question specifically stated "Naturally aspirated". Even so, with a turbo/supercharged engine, the answer would be the same. That's exactly the "faster air" that Mule is talking about.

Originally Posted by Mule

Dude, I had an argument about this with a real genius (who claimed to have built racing engines) about this very topic on the 928 board. He claimed the air "runs in." I said cool. I'll save money on a turbo & just get faster air. Here is the simple explanation. .....

Yeah, I understand the how. The thing is how to describe/demonstrate to someone that it's the air pressure pushing and not the piston sucking. I guess maybe the theory is that a vacuum, being nothing, can't really suck, but that air molecules moving around will eventually move to fill a void. So from that point of view, a vacuum can't "do" anything, but air which is moving, is doing a lot.

[Drago]

Originally Posted by island911

yeah, they are a bit sensitive to the word. ...usually used as my physics class Sucks!.

seriously, that Q sucked as well. My first thought was 'sucking is just the creation of a pressure differential' . . .my second thought, 'what if the engine is supercharged?' ..third thought, 'well I should just check the box of what I think that they think the answer is.'

So Island, are you speaking of the classes you've taught or the ones you've taken?

I flew through it and scored worse than most of you, which may reflect on my not finishing my engineering degree years ago.

Good thing they still let me design things that you guys fly, and fly in.

[Drago]

Originally Posted by Danny_Ocean

Hmmm...I bombed the "guess the weight" questions (pulleys), but aced the electrical.

I was the opposite.

Electrons and I do not get along easily.

[Flatbutt1]

I found tracing electrical current and gear directions amongst the easiest questions. I screwed up thing like the aspirated question, psi on the piston base, and calculating some of the forces(doing them in my head anyways)

[futuresoptions]

Took it again and scored an 84 but couldn't figure out what questions I was getting wrong. It did not show me and I hit exit and it took me to the Diesel engine page.

[lendaddy]

Originally Posted by futuresoptions

Took it again and scored an 84 but couldn't figure out what questions I was getting wrong. It did not show me and I hit exit and it took me to the Diesel engine page.

top right is a small icon for "review test"