Mechanical aptitude test...for fun.
AudiWorld Senior Member
Joined: Sep 2005
Posts: 1,394
Likes: 0
Kinda stupid. Force isn't measured in 'kg'... Force isn't measured in PSI, either.
Many of the questions were way too ambiguous for me to know what they wanted for an answer, and relative motions, etc. were just assumption.
Def not a physics, statics, dynamics or thermo exam... :P
Def not a physics, statics, dynamics or thermo exam... :P
AudiWorld Super User
Joined: Jul 2006
Posts: 5,641
Likes: 0
the hydraulic piston question, has the wrong answers...
the one where the size of the piston is diff and they ask how much force is exerted on the smaller bottom piston. It should be less, but all the answers were more.
Trending Topics
AudiWorld Super User
Joined: Jul 2006
Posts: 5,641
Likes: 0
hmm... I'm thinking of like a hydraulic floor jack....
where by lets say thru the handle and its mechanical advantage, you can exert 300 lbs of force on the SMALL piston. Lets say the small piston bore is... oh, 3 sqrt-inches. So you get:
300 lbs / 3 sqrt-inch = 100 psi of hydraulic pressure.
Hydraulic pressure, being incompressible, will be constant at the face of the main LARGE piston also... the large piston that lifts the car up. And lets say that large piston has a bore that's 5x the smaller piston bore, so 15 sq-inches. So then the force the large piston will exert:
100 psi * 15 sq-inch = 1500 lbs!
or 3x the force on the smaller piston, which is exactly the ratio of areas between the piston bores. (And that force is at the piston, add/subtract mechanical leverage to the floor jack tray... also the piston size numbers are out of my... ug... ****! But they are definitely 2 very different sizes.)
Thus given constant hydraulic pressure, the more surface area, the more force.
At least that's how I read the problem in that test. Like Pscheoverdrive said, the wordings are very ambiguous... so I may have totally read the problem wrong!
For one, they gave the "force" in "psi", which is incorrect.
300 lbs / 3 sqrt-inch = 100 psi of hydraulic pressure.
Hydraulic pressure, being incompressible, will be constant at the face of the main LARGE piston also... the large piston that lifts the car up. And lets say that large piston has a bore that's 5x the smaller piston bore, so 15 sq-inches. So then the force the large piston will exert:
100 psi * 15 sq-inch = 1500 lbs!
or 3x the force on the smaller piston, which is exactly the ratio of areas between the piston bores. (And that force is at the piston, add/subtract mechanical leverage to the floor jack tray... also the piston size numbers are out of my... ug... ****! But they are definitely 2 very different sizes.)
Thus given constant hydraulic pressure, the more surface area, the more force.
At least that's how I read the problem in that test. Like Pscheoverdrive said, the wordings are very ambiguous... so I may have totally read the problem wrong!
For one, they gave the "force" in "psi", which is incorrect.
AudiWorld Stories
Bringing Audi to Life for Audi Fans
Top 10 Most Expensive Audis Ever Sold on Bring-A-Trailer
Brett Foote
10 Audi Features & Options We Miss the Most!
Joe Kucinski
Audi Recreates Crazy-Looking Speed Record Breaker From 1935
Verdad Gallardo
Coachbuilder Recreates the 1995 Audi TTS Concept
Verdad Gallardo
Every Audi V10 Car Ranked!
Joe Kucinski
9 Audi Designs That Aged Like Fine Wine
Verdad Gallardo
2026 Audi Q5 Buyer's Guide (Every Model Explained)
Brett Foote
Ranking Every Current Audi 'S' Model From Worst to First!
Joe Kucinski
10 Best Audis That are FINALLY LEGAL to Import to the U.S.!
Joe Kucinski
Thread Starter
AudiWorld Super User
Joined: Dec 2000
Posts: 21,313
Likes: 1
In theory, you could use a floor jack to weigh a car...
Thread a pressure gauge into the hydraulic cylinder, jack up the front just to clear the wheels from the ground, then repeat for the rears, recording both pressure values. Then accurately measured the cylinder piston diameter (the one that comes out of the cylinder chamber). Then it's just:
Pressure (lb/in²) * Area of piston (in²) = Force (lb)
Only problem is the numbers won't be accurate if the vehicle isn't level when in the jacked position. You could get angle measurements and do some calc's based on CG measurements, but that starts sounding like work. :P
And yes the 'test' wasn't worded well...the fate of our careers doesn't rest on the pass/fail of it.
Pressure (lb/in²) * Area of piston (in²) = Force (lb)
Only problem is the numbers won't be accurate if the vehicle isn't level when in the jacked position. You could get angle measurements and do some calc's based on CG measurements, but that starts sounding like work. :P
And yes the 'test' wasn't worded well...the fate of our careers doesn't rest on the pass/fail of it.
Thread
Thread Starter
Forum
Replies
Last Post
brjones
A4 (B8 Platform) Discussion
16
Oct 7, 2015 08:17 PM
