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Homework Help: Potential Grav. Energy to Kine. Energy Problem

  1. Aug 8, 2009 #1
    1. The problem statement, all variables and given/known data
    On a roller coaster ride the total mass of the cart - with passengers included - is 280 kg. Peak K is at 46.0 m above the ground, peak L is at 21.5 m. The speed of the cart at K is 17.1 m/s, at L it is 12.8 m/s. How much energy is lost due to friction between the two peaks?

    2. Relevant equations
    Ke = 1/2mv^2 = mgh

    3. The attempt at a solution
    I tried finding the Ke at the 2 different points and subtracting.. it didn't work .
    then i tried with the mgh and subtracted it, and it still didn't work.
    So i guess i'm confused on which of the given data i should use.

    Thanks alot!
  2. jcsd
  3. Aug 8, 2009 #2

    Doc Al

    User Avatar

    Staff: Mentor

    Compare the total energy (KE + PE) at the two points.
  4. Aug 8, 2009 #3
    i see. I got 85000, which was right.
    Thanks again
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