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 Foo Off-Topic chit chat with no general subject.

 01-18-07, 02:25 PM #1 phantomcow2 la vache fantôme Thread Starter     Join Date: Aug 2004 Location: NH Bikes: Posts: 6,266 Mentioned: 0 Post(s) Tagged: 0 Thread(s) Quoted: 1 Post(s) I am clueless when it comes to solving this This was a test question today. What pisses me off is that I have solved a problem almost exactly like this before, a few months ago. I can't remember at all how I did it "A car is driving in a circuit with a radius of 35m, what is the max velocity it could be traveling at? Coefficient friction is .453". Any ideas? Something to jump start my mind? __________________ C://dos C://dos.run run.dos.run
 01-18-07, 02:27 PM #2 Taerom Hazardous     Join Date: Jun 2005 Location: Quarantine Bikes: 2005 Trek Liquid 55, 2009 Haro Mary SS Posts: 727 Mentioned: 0 Post(s) Tagged: 0 Thread(s) Quoted: 0 Post(s) What kind of car is it?
01-18-07, 02:37 PM   #3
divergence
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Quote:
 Originally Posted by phantomcow2 This was a test question today. What pisses me off is that I have solved a problem almost exactly like this before, a few months ago. I can't remember at all how I did it "A car is driving in a circuit with a radius of 35m, what is the max velocity it could be traveling at? Coefficient friction is .453". Any ideas? Something to jump start my mind?
If the track surface is level (rather than banked), then the normal force on the car is equal to its weight mg (where m=car's mass, g = gravitational field). Maximum force of friction is the coefficient of friction times the normal force.

Meanwhile, the force needed for the car to navigate the circle is its mass m times the centripetal acceleration v^2/r.

The car is driving at the maximum possible speed when the needed force (mv^2/r) equals the maximum possible force (mg times the coefficient of friction).

So set these two expressions equal, notice that the car's mass m cancels out (which is good, since they didn't give it to you), and solve for v.

 01-18-07, 04:16 PM #4 nobrainer440 I play in the street.     Join Date: Jul 2005 Location: College: K-State; Home: Overland Park, KS Bikes: 2005 Allez Triple, 1971 Schwinn Varsity Fixed Gear Conversion Posts: 977 Mentioned: 0 Post(s) Tagged: 0 Thread(s) Quoted: 0 Post(s) (max. force due to friction) = (coeff of friction) * (normal force) f = m*a a = v^2 / r I think those should do it.
01-18-07, 04:22 PM   #5
jsharr
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Quote:
 Originally Posted by Taerom What kind of car is it?
and what color?
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 Originally Posted by colorider Phobias are for irrational fears. Fear of junk ripping badgers is perfectly rational. Those things are nasty.

01-18-07, 04:22 PM   #6
Taerom
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 Originally Posted by jsharr and what color?
Yeah, cuz red cars are always the fastest!

 01-18-07, 06:07 PM #7 DannoXYZ  Senior Member     Join Date: Jul 2005 Location: Saratoga, CA Bikes: Posts: 11,633 Mentioned: 0 Post(s) Tagged: 0 Thread(s) Quoted: 38 Post(s) This is the same problem as the carnival ride where you slide up a vertical wall on the spinning platform. At a certain speed, you stick to the wall and don't slide down... NoBrainer's equations are all you need... Don't get hung up on the mass units as they cancel out... good way to double-check your work as well. Write out each step and include the units and show your work...
 01-18-07, 06:09 PM #8 msheron I-M-D bell curve of bikn'   Join Date: Dec 2005 Location: NC mountains Bikes: 06' Jamis Eclipse in the making. Posts: 2,926 Mentioned: 0 Post(s) Tagged: 0 Thread(s) Quoted: 0 Post(s) Does the car have abs brakes and how heavy is the driver? __________________ Ego Campana Inflectum of Circuitous
01-18-07, 06:13 PM   #9
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 Originally Posted by Taerom Yeah, cuz red cars are always the fastest!
Don't be silly. What is playing on the radio at the time?
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 01-18-07, 08:55 PM #10 phantomcow2 la vache fantôme Thread Starter     Join Date: Aug 2004 Location: NH Bikes: Posts: 6,266 Mentioned: 0 Post(s) Tagged: 0 Thread(s) Quoted: 1 Post(s) . The worse part is that I wrote down nobrainers equations, I got that far. If I had spent all of 3 more minutes thinking about this I would have solved it. I feel like I ran a marathon but stopped 20ft before the finish line. __________________ C://dos C://dos.run run.dos.run
01-18-07, 09:22 PM   #11
jsharr
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 Originally Posted by chipcom Don't be silly. What is playing on the radio at the time?
This on an endless loop.
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 Originally Posted by colorider Phobias are for irrational fears. Fear of junk ripping badgers is perfectly rational. Those things are nasty.

 01-18-07, 09:31 PM #12 Turboem1 Banned.     Join Date: Aug 2006 Location: Long Island Bikes: Lemond Reno Posts: 883 Mentioned: 0 Post(s) Tagged: 0 Thread(s) Quoted: 0 Post(s) If my calculations are correct, when this baby hits eighty-eight miles per hour... you're gonna see some serious ****.