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Find the Min and Max Speed

  1. Dec 4, 2007 #1
    1. The problem statement, all variables and given/known data



    2. Relevant equations

    I draw free body diagram but I cannot attempt to go from there. Help Please.

    3. The attempt at a solution

    I have found the mui with no friction but that is not relevant to finding the answer. I have spent 25 hours on this question. Please just someone help me.
     
    Last edited: Dec 4, 2007
  2. jcsd
  3. Dec 4, 2007 #2

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    Frictional force = centripetal force. Assume some m for mass of car. Write the eqn.
     
  4. Dec 4, 2007 #3
    im still lostt.
     
  5. Dec 4, 2007 #4

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    The car is moving on a circular curve, and so there must be a centripetal force acting on it. The only force that prevents the car from flying off is the force of friction between the wheel and the road, acting inward.

    Frictional force F = mv^2/r. Also, F = kN = kmg, where k is co-eff of friction. Can you do it now? Remember, s = r*theta.
     
  6. Dec 4, 2007 #5
    Shooting can u please check your email no clue. How many Free body diagrams must I draw. 2. I still cannot understand.
     
  7. Dec 4, 2007 #6

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    s, the arc length, is given as 200 m and theta as 30 deg. So, you can find r, right? Convert 30 deg to radians.

    After that just plug in the values given in the formula I've given: mv^2/r = kmg.
    That shouldn't be too difficult. You'll get the max speed.
     
  8. Dec 4, 2007 #7
    Are you sure you copied the question exactly?

    I ask because if the car were on a flat surface, I don't see how there could be a Vmin for this problem (unless I'm missing something here).

    If I'm right then I would guess it's more likely that the 30 degrees is the slope the car is on, in which case Vmin will be the speed which gives the centripetal force that perfectly cancels frictional force (when it is acting inwards) and likewise for Vmax assuming an outward acting frictional force.
     
    Last edited: Dec 4, 2007
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