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Finding forces on a car rounding a curve

  1. Feb 21, 2013 #1
    1. The problem statement, all variables and given/known data
    A car with mass of 1200kg turns sharply with a radius of 40m and at 15/ms. The tires have a static friction of 0.9, rolling at 0.6 and kinetic at 0.3.

    1) how long does it take to make a turn at half a circle.
    2) what is the magnitude of frictional force on the tires in the turn
    3) After the turn, the car accelerates to 40m/s, assuming the divers uses max acceleration from friction, how long does it take to reach the new speed.
    4) the driver takes another curve at 40 m/s with a radius of 80 and skids. the roads are banked. what angles does the road need to be banked to prevent skidding.


    2. Relevant equations
    F=ma
    mv^2/r


    3. The attempt at a solution

    a) t=[itex]\frac{2\Pi R}{v}[/itex]= [itex]\frac{2 Pi (40)}{15}[/itex] so 16.75 seconds

    b) F=ma
    F[itex]_{smax}=[/itex]1200[itex]\frac{v^2}{r}[/itex]
    F[itex]_{smax}=[/itex]1200[itex]\frac{15^2}{40}[/itex]
    =6750N
    c) have no clue how to do C....im not sure how to go about it...

    D) arctan ∅= [itex]\frac{v^2}{gR}[/itex]

    arctan ∅ [itex]\frac{40^2}{-9.8m/s*80}[/itex]

    I get theta 1.11° degrees but that seems kindsa low.
     
    Last edited: Feb 21, 2013
  2. jcsd
  3. Feb 21, 2013 #2

    mfb

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    Staff: Mentor

    1/a: half a circle, not a full circle.
    2/b: I agree
    3/c: Given the coefficient of friction, what is the maximal horizontal force between car and ground?
    4/d: Did you draw a sketch?

    In general, keeping the units everywhere can help to spot mistakes.
     
  4. Feb 21, 2013 #3

    haruspex

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    No, 1.11 radians.
     
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