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TRDejaVu
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tony barnhill said:
UTC with a DST conversion factor.
terriphill
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72% failed but passed my expectations! Never turned a wrench until I bought my midget. I'm glad to see I was right about the piston.
94% and I don't agree with the "suction" question (48). As I recall in chemistry they said that everything had to do with atmospheric pressure and that vaccum didn't exist. I figured that the Ford people would use good common sense and not "ivory tower" terms!
I also disagree with their pully reduction numbers!
Bill
I also disagree with their pully reduction numbers!
Bill
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I got 96.
I noticed that one question, the two weights labeled A and B on the seesaw, where they are not equally spaced from the pivot, didn't have a correct answer among the choices. Weight A is centered one unit from the pivot, weight B is centered five units from the pivot. With A being 300 Kg, B should be 300/5=60 Kg.
Or maybe I misread something. As you say, can't go back & check.
I noticed that one question, the two weights labeled A and B on the seesaw, where they are not equally spaced from the pivot, didn't have a correct answer among the choices. Weight A is centered one unit from the pivot, weight B is centered five units from the pivot. With A being 300 Kg, B should be 300/5=60 Kg.
Or maybe I misread something. As you say, can't go back & check.
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<div class="ubbcode-block"><div class="ubbcode-header">Quote:] I don't agree with the "suction" question (48).[/QUOTE]
Yes, I thoroughly agree. I answered "suction," thinking that's what they expected, but there is really no such thing; it's atmospheric pressure that moves the air. Maybe that's one I got wrong because I was trying to be too clever.
Yes, I thoroughly agree. I answered "suction," thinking that's what they expected, but there is really no such thing; it's atmospheric pressure that moves the air. Maybe that's one I got wrong because I was trying to be too clever.
JamesWilson
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Sarastro said:
I think you were right with "suction".
Its the movement of the piston that creates a pressure differential.
As shown at that position its moving downwards creating less pressure (what I'd call suction); if shown at that same position moving upward it'd be creating more pressure (what I'd call compression).
The atmospheric pressure is constant.
The air movement is caused by corresponding movements of the piston.
Its the piston that displaces the air- not the atmospheric pressure forcing air to move the piston.
No piston movement = no air movement.
Inertia applies: things at rest remain at rest until something external (i.e., the piston) causes them to move.
Any piston movement = pressure difference, and air movement.
Designing a good multiple choice question is more difficult than many people realize- not only does the right answer have to be right, the wrong ones have to look like they might be right too. Here's one I think the designer got wrong.
Twosheds
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Sarastro said:
How true!
Unless you are a follower of Lawsonomy, there is no such thing as suction.
If one of my students said, "suction", I would whomp him up side the hay-id, just as if he had said that volts flow.
Not really, but I would humorously threaten my students with a whomping, and I think it made them remember.
I chose the suction answer because I didn't have the test writer as a student.
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4-stroke engine principle = suck, squeeze, bang, blow.
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Suction vs. atmospheric pressure.....
I think we all understand the issue, but the discussion shows me that the choice of the correct answer is more semantics than mechanics. Both could arguably be correct, even though I don't like the "suction" description. That's not a good situation on a test.
I still remember, in high school, when one guy in my physics class made the mistake of saying that a vacuum caused something. The teacher shot back with the point that a vacuum is nothing--so how can it do something? A good lesson that technical descriptions require a certain precision.
I think we all understand the issue, but the discussion shows me that the choice of the correct answer is more semantics than mechanics. Both could arguably be correct, even though I don't like the "suction" description. That's not a good situation on a test.
I still remember, in high school, when one guy in my physics class made the mistake of saying that a vacuum caused something. The teacher shot back with the point that a vacuum is nothing--so how can it do something? A good lesson that technical descriptions require a certain precision.
JamesWilson
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<div class="ubbcode-block"><div class="ubbcode-header">Quote:]... the correct answer is more semantics than mechanics[/QUOTE]
/bcforum/images/%%GRAEMLIN_URL%%/iagree.gif
<div class="ubbcode-block"><div class="ubbcode-header">Quote:]
In a naturally aspirated engine, air enters the cylinder ____________.
<ul>[*]because of gravity
[*]from suction caused by the piston going down
[*]from atmospheric pressure pushing it in.
[*]because of compression[/list]
[/QUOTE]
A very badly worded question.
Leaving suction out of it...
No piston movement: no air movement.
I wonder if the piston were traveling upwards how thay'd say the lower atmospheric pressure influenced air movement then?
/bcforum/images/%%GRAEMLIN_URL%%/iagree.gif
<div class="ubbcode-block"><div class="ubbcode-header">Quote:]
In a naturally aspirated engine, air enters the cylinder ____________.
<ul>[*]because of gravity
[*]from suction caused by the piston going down
[*]from atmospheric pressure pushing it in.
[*]because of compression[/list]
[/QUOTE]
A very badly worded question.
Leaving suction out of it...
No piston movement: no air movement.
I wonder if the piston were traveling upwards how thay'd say the lower atmospheric pressure influenced air movement then?
Twosheds
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<div class="ubbcode-block"><div class="ubbcode-header">Quote:]
A very badly worded question.
Leaving suction out of it...
No piston movement: no air movement.
I wonder if the piston were traveling upwards how thay'd say the lower atmospheric pressure influenced air movement then? [/QUOTE]
I agree that the question is bad.
I like discussing this kind of thing. If you want me to shut up, though, I will.
You make a good point about the piston movement. I think of it this way, though:
Energy is required to produce movement. Air pressure is a form of potential energy. The higher atmospheric pressure contains more potential energy than the lower pressure in the cylinder. So the higher pressure in the atmosphere causes the air to flow into the cylinder as the potential energy in the atmosphere turns into kinetic energy from the air moving. So the movement of air comes from the energy in the atmosphere.
Think of a tank of air at higher than atmospheric pressure. The cylinder contains more potential energy than the atmosphere because energy was used to compress the air in the tank. The air in the tank then containes potential energy. If you open the valve, air flows out and the potential energy of the air in the tank becomes kinetic energy.
A very badly worded question.
Leaving suction out of it...
No piston movement: no air movement.
I wonder if the piston were traveling upwards how thay'd say the lower atmospheric pressure influenced air movement then? [/QUOTE]
I agree that the question is bad.
I like discussing this kind of thing. If you want me to shut up, though, I will.
You make a good point about the piston movement. I think of it this way, though:
Energy is required to produce movement. Air pressure is a form of potential energy. The higher atmospheric pressure contains more potential energy than the lower pressure in the cylinder. So the higher pressure in the atmosphere causes the air to flow into the cylinder as the potential energy in the atmosphere turns into kinetic energy from the air moving. So the movement of air comes from the energy in the atmosphere.
Think of a tank of air at higher than atmospheric pressure. The cylinder contains more potential energy than the atmosphere because energy was used to compress the air in the tank. The air in the tank then containes potential energy. If you open the valve, air flows out and the potential energy of the air in the tank becomes kinetic energy.
racingenglishcars
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Question 16,17. Force is measured in Newtons. Not in kg. Plus the cable is at an angle and will increase the necessary force to more than 1/2 that of the mass.
Question 30 does not have a correct answer within the available choices. Center of mass of box A is one unit from the pivot. Center of mass of box B is 5 units from the pivot. Box A weighs 300 kg therefore box B weighs 300/5 = 60 kg.
Question 41 asks for what force is at the bottom of the piston, while the answers want a pressure in PSI. Force is measured in pounds-force or Newtons.
For which reason I only got 98%
Question 30 does not have a correct answer within the available choices. Center of mass of box A is one unit from the pivot. Center of mass of box B is 5 units from the pivot. Box A weighs 300 kg therefore box B weighs 300/5 = 60 kg.
Question 41 asks for what force is at the bottom of the piston, while the answers want a pressure in PSI. Force is measured in pounds-force or Newtons.
For which reason I only got 98%
racingenglishcars
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JamesWilson said:
As the piston decends, the pressure container merely becomes larger. Assuming the contained gas quantity remains constant, the pressure will drop, along with the temperature (pv=nRT).
Being a lower pressure container, with an open inlet valve, the higher pressure (atmospheric) air will force its way in.
When the piston travels "upward", the container is reduced in volume and the pressure is increased. When the pressure is higher than atmospheric, and a valve is open, the higher pressure air forces its way to the atmosphere.
And Steve. After writing my previous post, I then read the thread and saw that you already mentioned the discrepancy in question 31.