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Roller Coaster Physics- Determining the highest point's height

  1. Mar 13, 2012 #1
    1. The problem statement, all variables and given/known data[/b
    ]Here’s what you know: Mass is 750 Kg, Velocity is 20 m/s, Gravity remains at 10 m/s2 and Point B’s height is 15 m. Assume that Point A is the highest point and assume there is no friction for this problem.

    Complete in the order that makes the best sense to you:
    Calculate the total energy at Point A and Point B. Determine Point A’s height.



    2. Relevant equations

    E= mgh + ½ mv2

    3. The attempt at a solution

    Energy at Point B: (+ 4 pts)
    E= mgh + ½ mv2
    E= (750) (10) (15) + 0
    E= 112500 J

    I found the Ep for Point B. When I tried to work "backwards" by trying to find Point A's height by using Point B's Ep and height, I came up with a negative energy. I think there should be a way to use this known data to determine point A's height and Ep, but I can not figure it out.
     
  2. jcsd
  3. Mar 13, 2012 #2

    cepheid

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    Welcome to PF angelbonnet,

    It's not clear what's going on in the problem. Does the roller coaster start at point A or at point B? At what point does it have the velocity of 20 m/s?

    If you can clarify these points, we should be able to help.
     
  4. Mar 13, 2012 #3
    Thank you, The roller coaster starts at point A and the velocity is for point B.
     
  5. Mar 13, 2012 #4

    cepheid

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    Okay, then your expression for the energy at point B is wrong, because you have not included the kinetic energy that the roller coaster has at point B due to its motion at 20 m/s.

    Total energy is conserved, so the potential energy that the coaster loses in falling from point A to point B must be equal to the kinetic energy that it gains as a result.

    You can use this fact to figure out what distance it must have fallen i.e. how much higher point A is than point B.
     
  6. Mar 13, 2012 #5
    Thank you for the insights. I'll attempt it with these in mind.
     
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