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Homework Help: Conservation of Energy Problem with friction

  1. Jan 12, 2012 #1
    Fritz Strobl thrilled the world when he won the gold medal in the Salt Lake City games of 2002 in a daring run down an alpine skiing course. The course had a vertical drop of 880 meters. Assume his highest speed was 140 km/h, and that he was moving at that speed at the end. (a) How fast would he have been moving if he could have "ignored" forces like air resistance and friction? (b) How much energy did he lose to forces like air resistance, friction, and so forth (assume his mass is 80 kg, and express the answer as a positive number)?

    So, I have that:
    Δx = 880 m
    vi=vf = 140 km/h = 38.9 m/s.
    g = 9.8 m/s2

    I known the equation for conservation of energy KEi +PEi = KEf+PEf

    I also know that W= F*Δx*cosθ

    I have no idea how to even start this problem. I do not know how to go about solving this. Please help! Thanks!
  2. jcsd
  3. Jan 12, 2012 #2
    For the first part imagine you push the skier out of a plane which is 880 meters above the ground and he falls without air resistance. How fast will he be going when it hits the ground? What is his kinetic energy before he hits the ground? Call that energy E

    For the second part calculate the skiers kinetic energy if he is going 140 km/h, call that energy e. The energy "lost" is E - e

    Hope that helps.
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