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Old 01-18-07, 02:25 PM   #1
phantomcow2
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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?
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Old 01-18-07, 02:27 PM   #2
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What kind of car is it?
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Old 01-18-07, 02:37 PM   #3
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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.
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Old 01-18-07, 04:16 PM   #4
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(max. force due to friction) = (coeff of friction) * (normal force)

f = m*a

a = v^2 / r

I think those should do it.
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Old 01-18-07, 04:22 PM   #5
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What kind of car is it?
and what color?
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Phobias are for irrational fears. Fear of junk ripping badgers is perfectly rational. Those things are nasty.
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Old 01-18-07, 04:22 PM   #6
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and what color?
Yeah, cuz red cars are always the fastest!
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Old 01-18-07, 06:07 PM   #7
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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...
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Old 01-18-07, 06:09 PM   #8
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Does the car have abs brakes and how heavy is the driver?
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Old 01-18-07, 06:13 PM   #9
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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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Old 01-18-07, 08:55 PM   #10
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. 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.
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Old 01-18-07, 09:22 PM   #11
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Don't be silly. What is playing on the radio at the time?
This on an endless loop.
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Old 01-18-07, 09:31 PM   #12
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If my calculations are correct, when this baby hits eighty-eight miles per hour... you're gonna see some serious ****.
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