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Homework Help: Another Centripetal Force Q

  1. May 22, 2010 #1
    1. The problem statement, all variables and given/known data
    A truck with a mass of 20000kg goes around a circular path with a speed of 50km/hr. If the radius is 105m. Calculate the centripetal force acting on the car.


    2. Relevant equations
    This is why I can't get the answer to this question. I don't know which equation to use. I'm thinking its Fc=4pi^2mrf^2, but I don't know the frequency and speed isn't in the equation so it's probably not the right equation.


    3. The attempt at a solution

    Fc= 4pi^2(20000)(105)f^2
     
  2. jcsd
  3. May 22, 2010 #2

    Doc Al

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    Staff: Mentor

    See: http://hyperphysics.phy-astr.gsu.edu/hbase/cf.html" [Broken]
     
    Last edited by a moderator: May 4, 2017
  4. May 22, 2010 #3
    So the answer would be F=(20000)(50^2/105)?
     
  5. May 22, 2010 #4
    Oh wait, it says velocity, not speed. How would you findd that then?
     
  6. May 23, 2010 #5
    speed refers to the magnitude of the velocity. SInce the problem requires you to find the MAGNITUDE of centripedal acceleration, the speed would be fine.
     
  7. May 23, 2010 #6

    Doc Al

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    Careful with units. Standard units for speed would be m/s, not km/hr.
     
  8. May 23, 2010 #7
    Alright, thanks alot for your help guys :)

    Final answer:
    F=(20000)([50x1000/60/60)^2]/105)
     
  9. May 24, 2010 #8
    The centre of the circular path exerts this centripetal force, correct?
     
  10. May 24, 2010 #9
    No. CPF itself doesnt have an existence. It comes into existence when a uniform circular motion takes place so as to balance the centrifugal force. It is always directed towards the centre though.
     
  11. May 24, 2010 #10

    Doc Al

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    No, it's the friction that exerts the centripetal force. That force points toward the center though.

    Sure it does. (Assuming by CPF you mean centripetal force.)
    There's no need to mention centrifugal force (which is a fictitious force), unless you are analyzing things from a non-inertial frame.
     
  12. May 24, 2010 #11
    I know that CFF is a pseudo force but doesn't CPF arise because of this false force?
     
  13. May 25, 2010 #12

    Doc Al

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    Pseudo forces only arise when applying Newton's laws in a non-inertial frame. Viewed from the usual inertial frame, centrifugal force never enters the picture. Something moving in a circle is centripetally accelerating; whatever force is causing that acceleration is labeled the centripetal force.
     
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