# Foo - I am clueless when it comes to solving this

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phantomcow2
01-18-07, 01:25 PM
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 :mad:
"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?

Taerom
01-18-07, 01:27 PM
What kind of car is it?

divergence
01-18-07, 01:37 PM
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 :mad:
"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.

nobrainer440
01-18-07, 03:16 PM
(max. force due to friction) = (coeff of friction) * (normal force)

f = m*a

a = v^2 / r

I think those should do it.

jsharr
01-18-07, 03:22 PM
What kind of car is it?
and what color?

Taerom
01-18-07, 03:22 PM
and what color?

Yeah, cuz red cars are always the fastest!

DannoXYZ
01-18-07, 05:07 PM
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...

msheron
01-18-07, 05:09 PM
Does the car have abs brakes and how heavy is the driver?

chipcom
01-18-07, 05:13 PM
Yeah, cuz red cars are always the fastest!

Don't be silly. What is playing on the radio at the time?

phantomcow2
01-18-07, 07:55 PM
:(. 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. :mad:

jsharr
01-18-07, 08:22 PM
Don't be silly. What is playing on the radio at the time?
This (http://www.youtube.com/watch?v=wb9ymusqTZI) on an endless loop.

Turboem1
01-18-07, 08:31 PM
If my calculations are correct, when this baby hits eighty-eight miles per hour... you're gonna see some serious ****.