Mechanical aptitude "test"

  • Thread starter Keef
  • 99 comments
  • 5,668 views
76%.

Messed up on a couple gear questions, a couple pulley questions.

I was also thinking that higher pressure in the smaller diameter tube would force more water into the cylinder... Apparently not.
 
96%

I misunderstood the lousy diagram for question 47, and I think their answer for number 48 is dead wrong. Atmospheric pressure will only force air into a cylinder because of the pressure differential caused when the piston drops, ie. Suction, just like loading a syringe.

I'm a bit annoyed

Keef
I think the only question I was completely clueless on was near the end, and was about water flowing through a pipe, running into a thing that increses its pressure, and asking which of two cylinders it would rise in. I've never even thought about a situation like that before. Where would something like that come into play?
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Slicks
I was also thinking that higher pressure in the smaller diameter tube would force more water into the cylinder... Apparently not.
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That one is all about the Bernoulli equation. The restriction increases the velocity of the flow to preserve the overall mass flow rate of the system. By increasing the velocity, the static pressure of the flow necessarily drops. If it didn't, you'd have an accumulation of mass in the narrower portion of the pipe (not to mention a number of other weird things going on in a world of broken physics... water flowing uphill and puddling at high points, kitchen faucets sucking all the air out of a room, toilets spewing your waste back at you, etc etc).

Bernoulli equation on Wikipedia - ignore the gz term, that only applies to situations where there is a net change in elevation over the control volume, which there wasn't in this question.


I know, more information than you really needed.
 
I am starting high school, and I got 60%! Wonder how those Honda F1 guys would have done...

Congratulations, Omnis! Maybe we should study together.
 
Sakiale
64 in 9th grade.. probably electricity and pulleys kilt me...
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casual%20kilt.JPG

Good thing they didn't include an English section.

thats a $285 kilt, by the way! :scared:
 
Omnis, how many times did you try? ;)

superberkut
Wonder how those Honda F1 guys would have done...
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They'd fail it.

Boundary Layer
I think their answer for number 48 is dead wrong. Atmospheric pressure will only force air into a cylinder because of the pressure differential caused when the piston drops, ie. Suction, just like loading a syringe.
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Same here, I believe atmo-pressure will only push air into it because the piston moves downwards, IE creates a low-pressure area.
 
I got an 80, much better than I expected seeing how other people did around here.

I have no idea about electrical circuits. A lot of guess work went into that one. Other than that, I had pulleys Junior year, and gears aren't that hard. Levers are pretty easy too. I don't really remember the other ones that gave me trouble. Not bad for a college freshman?

Oh and good job Onmis, Metar and BL!👍
 
Circuits are pretty easy once you get the hang of them. I studied that two years ago, but it's not too difficult.

A serial connection is, as the name implies, more than one power-using part coupled straight. Parallel is the opposite - with both power-users having a "personal" connection to the battery that doesn't have anything to do with the other part. In a serial connection, disconnecting one would shut down the other. In a parallel, the other would continue functioning.

In a serial connection, voltage is built up at each powersource - as the two serial batteries show, the voltage at the voltmeter will read 24. Meanwhile, ampere-readings will be the same as the ampere-values that each battery produces. In a parallel connection, voltage remains the same as the value each of the batteries is producing (IE, 12V in this case), while ampere-readings will be the sum of values each battery is producing. Doesn't sound simple, but actually is.
 
Metar
Omnis, how many times did you try? ;)
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Just once. I was a little iffy with the piston suction question, though-- kind of a fluke that I got it right.
 
I'm still happy with the score I got for it being nearly 2am or something.

Boundary Layer
That one is all about the Bernoulli equation. The restriction increases the velocity of the flow to preserve the overall mass flow rate of the system. By increasing the velocity, the static pressure of the flow necessarily drops. If it didn't, you'd have an accumulation of mass in the narrower portion of the pipe (not to mention a number of other weird things going on in a world of broken physics... water flowing uphill and puddling at high points, kitchen faucets sucking all the air out of a room, toilets spewing your waste back at you, etc etc).

Bernoulli equation on Wikipedia - ignore the gz term, that only applies to situations where there is a net change in elevation over the control volume, which there wasn't in this question.

I know, more information than you really needed.
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You aren't an HVAC, are you? :P
 
The second time I did two better, I got an 82.

I did great on the electrical stuff. Circuit diagrams are easy. I got my adding of potential mixed around the first time. That's from physics last year. The belts were fun.
 
I got an 80% just now on my second try.

But I've got a gripe with the question about why air enters a cylinder during the intake stroke. If the valve opened before TDC the air would not start entering until the piston started sucking it down. If the intake valve opened after TDC the air would be pushed in to fill that low-pressure zone. So which comes first: The suction required to make a low-pressure zone, or the force pushing the air to fill that zone?
 
Keef
So which comes first: The suction required to make a low-pressure zone, or the force pushing the air to fill that zone?
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Actually, it doesn't matter which comes first as long as both come.

And it's the difference between atmo-pressure and the low pressure the cylinder creates, as you said correctly...
 
I understand that the reason air enters is both outside pressure and suction, but I'm confused why the question made you pick one or the other.
 
Keef
I understand that the reason air enters is both outside pressure and suction, but I'm confused why the question made you pick one or the other.
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Because it's stupid? 💡

A good question is built to make you think, but ultimately reach the single correct answer. This one has two equally-correct.

I guess they assume the valve opens after the piston is lowered.
 
Ever heard of sarcasm? Not exactly a new concept but once you get the hang of it you'll enjoy it.👍
 
I got around question 20 and quit cause it's nearly 2 am, but it was very very easy up to that point.

Why is everyone getting low grades?
 
58%, with practically zero knowledge to the majority of the sections. For a lot of them I tried to visualize the diagrams in 3D.
 

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