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Circular Motion

  1. Dec 15, 2013 #1
    1. The problem statement, all variables and given/known data



    2. Relevant equations



    3. The attempt at a solution
    I have found the solution to part(B)
    But I don't understand why the centripetal force is equal to the weight of the vehicle when the speed of the vehicle is maximum.
     

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  2. jcsd
  3. Dec 15, 2013 #2


    Do you mean maximum? The minimum speed would be zero.
     
  4. Dec 15, 2013 #3
    Yes.Sorry for my typo
     
  5. Dec 15, 2013 #4
    Okay. So, what would happen if the centripetal force became greater than the weight?
     
  6. Dec 15, 2013 #5

    Doc Al

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    What are the only forces acting on the vehicle?
     
  7. Dec 15, 2013 #6
    I don't know:frown:
     
  8. Dec 15, 2013 #7
    Centripetal force and tangential force?
     
  9. Dec 15, 2013 #8

    Doc Al

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    No, I'm talking about real forces. ("Centripetal force" is just the name given to whatever force is producing the centripetal acceleration. It's not a kind of force.)

    Hint: One of those forces is gravity. What's the other? (I'm only interesting in forces that act at the top of the motion.)
     
  10. Dec 15, 2013 #9
    Normal force? But I don't know how they are relevant to the maximum speed:cry:
     
  11. Dec 15, 2013 #10

    Doc Al

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    Yes!

    They are relevant because those two forces combine to give you the centripetal force.

    What direction do those forces act? Express the centripetal force in terms of those forces.

    The force of gravity cannot change, but what about the normal force?
     
  12. Dec 15, 2013 #11
    Am I correct?
    But when the centripetal force is greater than the weight, the normal force will be smaller than zero.
    Is it correct?
     

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  13. Dec 15, 2013 #12

    Doc Al

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    Yes.

    Of course the normal force cannot be less than zero. What will happen is that the vehicle will leave the track if the speed is too great. The point where it is going as fast as it can and still maintain contact will be when the normal force goes to zero.
     
  14. Dec 15, 2013 #13
    Why the vehicle will leave the track when the normal force becomes zero?
    Sorry for my stupidity.:shy:
     
  15. Dec 15, 2013 #14

    Doc Al

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    As long as the vehicle is pressing against the track there will be a normal force. When the normal force goes to zero, that means it is no longer pressing against the track--if it goes any faster, it begins to go flying off.
     
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