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Homework Help: Help with Kinetic and Potential Energy

  1. Oct 27, 2007 #1
    1. The problem statement, all variables and given/known data

    A 51.0 skateboarder wants to just make it to the upper edge of a "quarter pipe," a track that is one-quarter of a circle with a radius of 3.30 . What speed does he need at the bottom?

    2. Relevant equations
    I have no idea where to start with this problem. Physics is sooo difficult for me!

    3. The attempt at a solution

    The furthest I got was to figure that length of the quarter pipe would be 5.184 m because one quarter of the circumference, which I calculated to be 20.735 m, would be 5.184m. I'm not sure if this was necessary or not.
  2. jcsd
  3. Oct 27, 2007 #2
    I am new to this site, and very greatful that such a site exists. Please let me know if I am not using the proper ettiquite.

  4. Oct 27, 2007 #3

    You are doing great. Before you try to solve the problem. always write down your given values and the values that your looking for as well as the equations required to solve this group ( Ke and PE problems). I have a question for you. From the given information do you know what your final velocity could be? That may be one of your given variables.:cool:
  5. Oct 27, 2007 #4
    Also, do you know if you are dealing with conservative or non-conservative forces etc.
  6. Oct 27, 2007 #5
    I assume it to be conservative forces because that is what we have been focusing on in class.
    The only given values for this problem are:
    the mass of the skateboarder = 51.0 kg
    the fact that the quarter pipe is one quarter of a circle with radius 3.30 m

    I am not sure how I would go about calculating the velocity in this case. I have a distance, but no time reference.


    KE = 1/2 mv^2
    U_g = mgy (gravitational energy)
    K_f + U_g_f = K_i + U_g_i
    E_mech = K + U (mechanical energy)
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