Mechanical aptitude test

[chimpboy]

Correct, lower than atmospheric pressure, not a true vacuum, hence there is no "real" suck, its a pressure differential, so the higher pressure, PUSHES the air in, it is not sucked in, for fark sake, maybe read some text on the matter, instead of me trying to convince you

I'm just telling you what the fact is, and why you got the question wrong

Leaving aside the obvious jokes, how would you define suction then?

If creating a low pressure zone so that higher pressure air moves into it is not sucking, then what is?

[cloughy]

Suction is the creation of a partial vacuum, or region of low pressure. The pressure gradient between this region and the ambient pressure will propel matter toward the low pressure area. Physicists consider the notion of "suction" to be specious, since vacuums do not innately attract matter. Dust being "sucked" into a vacuum cleaner is actually being pushed in by the higher pressure air on the outside of the cleaner.

Higher pressure of surrounding air can push matter into a vacuum but a vacuum cannot attract matter.


http://en.wikipedia.org/wiki/Suction

I'm not good at explanation's I just know I'm right

[dumbdunce]

I get 49/50 in a very quick attempt, how can you find out which one(s) you (allegedly) get wrong??

there are some bad questions like 31 with the COG of the boxes on the ends of the lever, and some liberal uses of terminology, confusing pressure with force, you have to step back and have a guess at the what they think is the parsimonious response.

shrug.

I change oil in trucks for a living, what would I know.

[Cruza62]

I'm not finished Uni yet (Engineering) thats my excuse.... 88% 440 points

Anyhow, suction does'nt exist.... where there is low pressure, there is usually a high pressure trying to fill its gap. Think about pushing your hand through water, on the trailing edge of your hand there is a whole heap of water trying to fill the void... consider the place where there is no water for that split second as the low pressure system i.e. the inside of the cylinder when the piston is going down makes a low pressure system and whatever can fill its space...will

Another one... When you "suck" on a straw, you are creating a low pressure system inside your mouth, therefore the higher pressure surrounding air will try to fill the low pressure system and go up the straw. So what if it is in some sort of liquid ie Jack n Coke.... when the end of the straw is in the liquid and you "suck" on the straw, once again you create that low pressure system in your mouth and the air surrounding the liquid will try and fill the low pressure system, but the liquid is in its way so it will push the liquid through the straw and eventually get to your mouth when there is no liquid left.

Another one... A plane works on this theory. The wing has a funny shape you will notice that the top isn't perfectly parrallel with the bottom (its not flat), the top is rounded and the bottom is flat. The shape of the wing (on top) causes the air on top to speed up and therefore causes a low pressure system, and once again the lift is caused by the higher pressure underneath the wing trying to fill the lower pressure system on top, and in the process forces the plane up...
Ben

[devo]

96%
got the spur gear going the wrong way
on question 44 why would there be fluid going up tube b ?

[-Scott-]

on question 44 why would there be fluid going up tube b ?

Because Professor Venturi said it would.

[dumbdunce]

I get 49/50 in a very quick attempt, how can you find out which one(s) you (allegedly) get wrong??

there are some bad questions like 31 with the COG of the boxes on the ends of the lever, and some liberal uses of terminology, confusing pressure with force, you have to step back and have a guess at the what they think is the parsimonious response.

shrug.

I change oil in trucks for a living, what would I know.

I took it again, 50/50, this time I found the review quiz button, so still none the wiser which one I got wrong the first time.

I still think some of the questions are 'wrong'.

[rusty_042]

haha im the dumbest one here i only got 72% not to bad considering i was only a 1st year mechanic working on mercades trucks an now work for a tel co lol

[-Scott-]

on question 44 why would there be fluid going up tube b ?

Because Professor Venturi said it would.

I've been thinking more about this one, and I believe I know the "school book" answer they want. But I suspect the real life answer would depend on the real life applied pressure &/or flow rate through the tube.

Any physicists here?

[Tapage]

I thought it's a really easy test .. I'm not thinking so much on it .. some question could be wrong of jbad pics ( draws ) ie .. the balloms ..

Or the spur gear.. just to get fun, don't you ?

[bad_religion_au]

Alright, i'll take the simple line (diesel not petrol) seeing as the site is about diesels, ....

so if there is no vacuum, how does the air fill the void, when the piston moves down?? wouldn't be atmospheric pressure would it.............

HUH. Vacuum, by definition IS a VOID... if there is no vacuum there is no VOID to fill???

Also no motor i'm familiar with uses butterflies to control airflow into the cylinder, they use valves

Righto, following what you've written, a diesel engine does not produce vacuum FACT, how the fark does the air get in there hey??

How the fark can valves be use to CONTROL airflow, they are used to time it and for how long, the amount of airflow (air/fuel) on a petrol engine is REGULATED by a butterfly and as stated before, diesel's are open to full atmosphere all the time, just the valves let air in for the required time and duration

Fark I hate argueing with learned people bloody uni students

Your talking about vacuum (or relative vacuum as chimpboy rightly points out) in the intake manifold i assume. in the actual cylinder, the piston moving down creates a region of lower than atmospheric pressure, which leads to the pressure difference required to see air move into the cylinder.

with no pressure difference between the atmosphere and the cylinder interior, you'd get no air movement, unless you had a compressor pushing air in... which would be turbo'd

we're saying the same thing, just a different way around .

[bad_religion_au]

I'm not finished Uni yet (Engineering) thats my excuse.... 88% 440 points

Anyhow, suction does'nt exist.... where there is low pressure, there is usually a high pressure trying to fill its gap. Think about pushing your hand through water, on the trailing edge of your hand there is a whole heap of water trying to fill the void... consider the place where there is no water for that split second as the low pressure system i.e. the inside of the cylinder when the piston is going down makes a low pressure system and whatever can fill its space...will

Another one... When you "suck" on a straw, you are creating a low pressure system inside your mouth, therefore the higher pressure surrounding air will try to fill the low pressure system and go up the straw. So what if it is in some sort of liquid ie Jack n Coke.... when the end of the straw is in the liquid and you "suck" on the straw, once again you create that low pressure system in your mouth and the air surrounding the liquid will try and fill the low pressure system, but the liquid is in its way so it will push the liquid through the straw and eventually get to your mouth when there is no liquid left.

Another one... A plane works on this theory. The wing has a funny shape you will notice that the top isn't perfectly parrallel with the bottom (its not flat), the top is rounded and the bottom is flat. The shape of the wing (on top) causes the air on top to speed up and therefore causes a low pressure system, and once again the lift is caused by the higher pressure underneath the wing trying to fill the lower pressure system on top, and in the process forces the plane up...
Ben

I know pressure systems etc, and i know that you can explain it from either way (the piston creates a low pressure system "sucking" air in or the alternative)

but the question is ambiguous. on one hand, you have them using the term "sucking in", which is wrong due to terminology (using sucking).

but the alternative is "due to atmospheric pressure".

this is also wrong, as one could read that answer to infer that atmospheric pressure fills the cylinder of all the air it needs at top dead center, as it doesn't include anything about "needing a low pressure area created by the falling piston".

[dumbdunce]

on question 44 why would there be fluid going up tube b ?

Because Professor Venturi said it would.

I've been thinking more about this one, and I believe I know the "school book" answer they want. But I suspect the real life answer would depend on the real life applied pressure &/or flow rate through the tube.

Any physicists here?

profesor venturi and the answer they want are both right. ther are various relative presssures to consider, ie the pressure in the neck of the venturi (and thus that vertical tube) relative to the pressure in the pipe upstream of the venturi (and thus that vertical tube), AND the pressures in the tube relative to atmosphere outside the tubes. from the diagram, we know the pressure in the pipe is higher than atmospheric at all points because the liquid in the tubes rises against atmospheric pressure.

It is probably confusing to anyone who has any understanding of carburettors because the fluids are on the 'wrong' sides, so the entire pressure balance is different.

bogged from wiki:

[Cruza62]

I suppose the terminology that is used is there for all who attempt the test understand what they are on about... not just physics people
Anyhow I think some of thr answers are a bit dodge... like the one where you have to work out the moment caused by the blocks on the rocking thingo, the centre og gravity isn't on the edge of the block, but this is where you have to calculate it from...?
I think this has been a good post, should be more like it and have comps..?
Ben

[devo]

bogged from wiki:

on the diagram they used it didnt have curved corners. they were sharp angles so i thought that would of causes a severe restriction at A with the pressure a 2 being lower so not pushing up tube b. if anything i was thinking this would cause air to be drawn down tube b not up.
oh well, not bad for a steering wheel attendent.

[dumbdunce]

on the diagram they used it didnt have curved corners. they were sharp angles so i thought that would of causes a severe restriction at A with the pressure a 2 being lower so not pushing up tube b. if anything i was thinking this would cause air to be drawn down tube b not up.
oh well, not bad for a steering wheel attendent.

venturi effect still happens whether the corners are curved or sharp, the cheapest venturi is an orifice plate that has very abrupt edges - still has similar pressure distribution, but a lot more turbulence.

[Cruza62]

The venturi thing...
The pressure in the pipe no matter where the holes or restricitions are, is greater than the pressure outside the pipe, (keep in mind that a gas is considered to have the same properties as a liquid ie convection etc) the gas (being the oxygen, in which you could consider just another liquid with a lesser density) has a lower pressure on it, therefore the higher pressure liquid (whatever is in the pipe, water etc) will fill the lower pressure (obviously in this case fighting against gravity), and this higher pressure is going to be wherever in the pipe, obviously the pressure at the first hole is greater than the second, but the second hole still has a higher pressure than gas above it, therefore it will rise..... is that a little easier to grasp.... don't worry, when I was first introduced to this I would of said the same thing
Ben

[bad_religion_au]

I suppose the terminology that is used is there for all who attempt the test understand what they are on about... not just physics people
Anyhow I think some of thr answers are a bit dodge... like the one where you have to work out the moment caused by the blocks on the rocking thingo, the centre og gravity isn't on the edge of the block, but this is where you have to calculate it from...?
I think this has been a good post, should be more like it and have comps..?
Ben

thats the problem. the "wrong" answer is only wrong from a purely physics terminology point of view, where the "right" answer disregards the pressure difference needed to fill the cylinder

[me3@neuralfibre.com]

on question 44 why would there be fluid going up tube b ?

Because Professor Venturi said it would.

I've been thinking more about this one, and I believe I know the "school book" answer they want. But I suspect the real life answer would depend on the real life applied pressure &/or flow rate through the tube.

Any physicists here?

profesor venturi and the answer they want are both right. ther are various relative presssures to consider, ie the pressure in the neck of the venturi (and thus that vertical tube) relative to the pressure in the pipe upstream of the venturi (and thus that vertical tube), AND the pressures in the tube relative to atmosphere outside the tubes. from the diagram, we know the pressure in the pipe is higher than atmospheric at all points because the liquid in the tubes rises against atmospheric pressure.

It is probably confusing to anyone who has any understanding of carburettors because the fluids are on the 'wrong' sides, so the entire pressure balance is different.

bogged from wiki:

Whilst this was my first thought, I have a spa bath that suck air into the pipes before it comes out the nozzles. There is enough pressure in the pipes to push the water over 2m if the noozzles are not underwater (and yes, it goes onto the bathroom floor). YET, they still draw air into the fittings that are 2" before each nozzle. The air is drawn straight from atmosphere through a control valve.

My venturi understanding is rusty, and bernoulli was wrong.
http://www.grc.nasa.gov/WWW/K-12/airplane/bernnew.html

Paul

[-Scott-]

Drifting further off topic...

My venturi understanding is rusty, and bernoulli was wrong.
http://www.grc.nasa.gov/WWW/K-12/airplane/bernnew.html

Paul

My venturi understanding isn't so much rusty as quite limited.

I read the link, but didn't see what makes bernoulli wrong?

[90Mav]

88% Bloody Spewing..
stuffed the pully ones..
and the venturi one...(thinking of a carb)
and misread the piston pressure one (thaught it said 100psi initial)
and the atsmopheric pressure one...

like i said... spewing..

[ISUZUROVER]

Drifting further off topic...

My venturi understanding is rusty, and bernoulli was wrong.
http://www.grc.nasa.gov/WWW/K-12/airplane/bernnew.html

Paul

My venturi understanding isn't so much rusty as quite limited.

I read the link, but didn't see what makes bernoulli wrong?

Scott - Bernoulli's theory basically boils down to pressure and velocity are inversely proportional. I.e - where velocity is high, pressure is low and vice versa. So BEFORE the venturi throat, the liquid is moving a vary low velocity and hence is at high pressure. Venturies (for air) are designed to reach speeds of 300 m/s through the constriction (throat) - so velocity is very high, and hence the pressure is ALWAYS reduced.

The link above is relating to a different application (something bernoulli never considered) - Bernoulli's relationship works for all applications he considered.

[shakes]

96%

Q8 - Sun gear - wording is very poor - rotates vs turns (I got confused)

Pulley questions - should say to neglect pulley friction

Q44 - Venturi - I don't beleive their answer. My spa bath shows very clearly water doesn't rise up the venturi tube. (second tube). First tube would rise due to static pressure before restriction.

But I am only an IT geek.
Paul

it's not static pressure that make's it rise dude, its the pressure difference... kinda like the suction argument

Large tube is low velocity high pressure (why the first tube rises), small tube is low pressure high velocity... you got something else wrong

How the hell can you get rotate and turn wrong when it come's to something round

how does pulley friction effect the weight when they are rounding to the nearest 25kg

But I'm only a dumb plumber that got 92% after 8 stubby's

[me3@neuralfibre.com]

how does pulley friction effect the weight when they are rounding to the nearest 25kg :rofl:

But I'm only a dumb plumber that got 92% after 8 stubby's :finger:

The question with the 3 pulleys and the ropes pulling from different angles. The question was which one would take the least force to lift (no quantities) , the answer was "all the same". Anyone who has been on a yacht knows that aint so, as block friction is not negligible.

Paul

[V8Patrol]

I'm not finished Uni yet (Engineering) thats my excuse.... 88% 440 points

I emailed the link to two so called 'qualified engineers' that I'm currently working with.......
You beat their scores

Anyhow, suction does'nt exist....

I have to work with engineers on a daily basis.......

Trust me .... engineers do SUCK !

Another one... When you "suck" on a straw, you are creating a low pressure system inside your mouth, ......

So I actually got 'low pressured off' for my birthday


The missus will be so impressed to hear that






Engineers are nothing but 'historians'.

they simply present old material that's worked in the past as the 'new design', its only when you question a design that they even bother to check it !
Which explains why it takes em 4 hours to return your call once you question a particular design section.... in reality they are actually crunching the numbers in order to check someone else's work that was done years ago!


What realy peaves me .......
You can buy a structral program and so design your own structures....problem is because you arent 'qualifed' the design must be signed off on by a qualified person.... thats using the exact same program !

You do all the work .......... they get the money

yep ...... it SUCKS


Kingy

[dumbdunce]

You do all the work .......... they get the money

sounds like a cry-baby, whinyassed opinion to me dude

if, as you imply, engineers are so lazy and stupid, how about you put aside a few years, go to uni, get yourself an engineering degree - should be easy since you can beat them in an online mechanical aptitude test - become an engineer, show them all how much better you can do it, then sit back and get all the money while someone else does all the work for you.

just a suggestion. you could show the UAC your score on this test to add weight to your application.

[cloughy]

You do all the work .......... they get the money

sounds like a cry-baby, whinyassed opinion to me dude

if, as you imply, engineers are so lazy and stupid, how about you put aside a few years, go to uni, get yourself an engineering degree - should be easy since you can beat them in an online mechanical aptitude test - become an engineer, show them all how much better you can do it, then sit back and get all the money while someone else does all the work for you.

just a suggestion. you could show the UAC your score on this test to add weight to your application.

[Cruza62]

Dude, I didn't get an email... anyhow
Scientists create stuff, engineers use the stuff to create other stuff. Thats the way it works... Often you may have a better way of doing something, thats good for you, but for anyone to take you seriously you need a bit of paper.....thats why i'm at uni...!
P.S. Uni (Engineering) is not just for learning physics and crazy maths, by the end of it you will approach problems with a different attitude. By the end of it you will think in a different way...
No need to degrade other peoples jobs, no-one sh!t cans you champ.
Ben

[cloughy]

Dude, I didn't get an email... anyhow
Scientists create stuff, engineers use the stuff to create other stuff. Thats the way it works... Often you may have a better way of doing something, thats good for you, but for anyone to take you seriously you need a bit of paper.....thats why i'm at uni...!
P.S. Uni (Engineering) is not just for learning physics and crazy maths, by the end of it you will approach problems with a different attitude. By the end of it you will think in a different way...
No need to degrade other peoples jobs, no-one sh!t cans you champ.
Ben

That's because if they did, it would be a cry-baby, whinyassed opinion

[chimpboy]

You do all the work .......... they get the money

yep ...... it SUCKS

I find that hard to believe, I thought that if you work hard and you're good your boss will always look after you?