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Homework Help: Work done by force.

  1. Nov 10, 2007 #1
    1. The problem statement, all variables and given/known data

    A 70.0 kg skier rides a 2700 m long lift to the top of a mountain. The lift makes an angle of 14.3° with the horizontal. What is the change in the skier's gravitational potential energy?
    in Joules

    2. Relevant equations

    3. The attempt at a solution

    I can't seem to find why Ef * s = mas
    does not work?

    i've tried using the equation for an answer and it doesn't seem to give me the right answer.
  2. jcsd
  3. Nov 10, 2007 #2
    What is the meaning of the symbols in "Ef * s = mas", especially the *?
  4. Nov 10, 2007 #3
    E = "work done by net ext. force

    s = displacement

    m = mass
    a = acceleration
  5. Nov 10, 2007 #4
    Thanks :-)

    The f and the * ?
  6. Nov 10, 2007 #5
    f = force and * = multiplication
  7. Nov 10, 2007 #6
    Thanks :-)

    * = multiplication, the same as between E and f, m and a, and a and s?

    If that's correct then the equation could be rewritten as
    Efs = mas
    which would be a strange equation because the s is useless; the equation is equivalent to
    Ef = ma
    and that can't be right because E, work/energy, is force times distance and ma is force so the equation would not be balanced -- the units would not be the same on each side. It would be saying
    force x distance x force x distance = force
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