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Roller Coaster analogy

  1. Jun 12, 2006 #1
    I'm not sure if this question belongs to this forum or advanced phsyics.. but since I'm still in high school, I think this is the right forum.

    I'm doing physics questions based on roller coaster and am just a little bit confused on how to answer some questions.

    You know :

    Mass of each empty car and with passangers
    Total length of track
    Slope of lift
    Horizontal distance from bottom of lift to top
    Change in elevation at first drop
    Track length at the first drop
    Length of each car

    Questions 1: Calculate the total energy required to raise the train to the top of the first hill

    I'm thinking Eg - Ek will give you the answer, but I'm not sure.

    A friend suggested that the energy required is simply 0 since the train is moving at constant velocity to the top of the hill.

    Question 2: Apply the law of conservation of energy to determine the speed of the first car at the bottom of the first hill, assuming some energy is lost in overcoming friction (use a reasonable estimate)

    I'm just dead confused about this one.

    Any help is appreciated!!
  2. jcsd
  3. Jun 12, 2006 #2
    To raise the coaster cars to a height h (using a chain drive perhaps) you need to do work against gravity. This energy is stored as potential energy at the top. Now when you come back down this energy is converted into kinetic energy. Thus there is constant shuttling of two different forms of energy. Now due to friction some energy is lost constantly (this is why the first dip of normal coasters is the tallest) and eventually the cars come to a stop.
    Can you do your question now ?
  4. Jun 12, 2006 #3
    Hm.... let me see if I get this right:

    Total energy to bring the train to the top = mgh

    That's it right?

    As for the second question, I'm still confused. I realize that the friction is causing energy loss.. but how do calculate the friction when you dont know the friction constant?
  5. Jun 12, 2006 #4


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    Yeah that's right.
    The question says, "use a resonable estimate", I would assume this means you can choose a co efficent. I believe the coefficenet of kinetic friction for steel on steel is around 0.6.
    Last edited: Jun 12, 2006
  6. Jun 12, 2006 #5
    Even if you have an approximate coefficient of kinetic friction, you would still need to know the slope of the track and not just the height .
  7. Jun 12, 2006 #6


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    I think that information is given in the question;
  8. Jun 12, 2006 #7
    Aww, shucks didn't notice that , sorry.
  9. Jun 12, 2006 #8


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    No problem, we all make silly mistake, including typos (RE projectile motion thread)...:wink:
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