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Help with an energy problem found on the Phet Website

  1. Feb 11, 2016 #1
    1. The problem statement, all variables and given/known data

    A 1000 kg roller coaster begins on a 10 m tall hill with an initial velocity of 6m/s and travels down before traveling up a second hill. As the coaster moves from its initial height to its lowest position, 1700J of energy is transformed to thermal energy by friction. In order for the roller coaster to safely travel over the second hill, it must be moving at a velocity of 4.6m/s or less at the top of the second hill. What is the maximum height the second hill can be?

    2. Relevant equations

    KE = .5mv2
    GPE = mgh
    total energy = PE + KE + The

    3. The attempt at a solution

    PEmax = Total energy
    PE = 1000kg (9.8 m/s2) 10m = 98,000J
    KE = .5 (1000 kg) 4.62 = 10,580 J

    Energy left at the bottom of the roller coaster = 98,000J - 1,700 J = 96,300 J

    96, 300 J - 10,580 J = 85,720J

    85,720 J = 1000kg (9.8 m/s2) h

    h = 8.75m
  2. jcsd
  3. Feb 11, 2016 #2


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    Homework Helper
    Gold Member

    The question is a bit strange, and I'm not sure whether it is a mistake or it is deliberately laying a trap.
    It provides a maximum speed for going over the second hill, but asks for a maximum height. Do you not see something odd about that?
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