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Homework Help: Banked Road Problem

  1. Oct 30, 2006 #1
    OK, last time I'll bother you guys today. I'm just having a tough time getting things to work out.

    A curve of radius 30m is banked so that a car can round the curve at 48km/h even if the road is frictionless. Calculate the banking angle theta for these conditions.

    I have;

    tan(theta) = v^2 / gr

    tan(theta) = 48^2 / (9.8 * 30)

    tan(theta) = 7.8367

    theta = 82.7 deg

    The book has 31 deg.

    Any ideas?

  2. jcsd
  3. Oct 30, 2006 #2
    48km/h is a dangerous thing to plug into an equation like that. As a habbit always plug the units in with their numbers
  4. Oct 30, 2006 #3
    You will have to convert 48 km/h to m/s. Or, convert 30m to km and 9.8 m/s^2 to km/hr^2.
  5. Oct 31, 2006 #4
    Argh, Thud, thud, thud ....
    (The sound of beating my head on the desk again.(

    That's the second time I made a units mistake last night. My montra for today will be "Check the units!"

  6. Sep 29, 2007 #5

    Okay, so I am doing a similar problem involving a car driving on a banked, circular track (theta=31degrees). I know that to find the centripetal acceleration, I am supposed to say that (mv^2)/r = nsin(theta). Then, I have to solve for n by saying that ncos(theta)=mg. However, I am confused... why can't n=mgcos(theta). My understanding is that two forces are equal in magnitude if the object doesn't move in either direction. The car doesn't move into the road or out of the road... or does it?? please help! I have a test on monday.
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