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Homework Help: Need help with a Work and Energy problem

  1. Dec 13, 2011 #1
    1. The problem statement, all variables and given/known data
    A car of weight 7000N travels at a steady speed of 8m/s up a steady incline at 15degrees above the horizontal. The car's motion is opposed by a constant frictional force of 500N.

    2. Relevant equations
    Calculate:
    a) the gain in p.e per second
    b) the work done per second against friction
    c) the car's engine power.

    3. The attempt at a solution
    I keep getting the wrong answer. It would be easier if I knew the distance traveled by the car but I don't know any suitable formula.

    Help is appreciated!
     
  2. jcsd
  3. Dec 13, 2011 #2

    PhanthomJay

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    Welcome to these forums!

    The car travels 8 m along the incline every second (given).
     
  4. Dec 13, 2011 #3
    In a way you do know the distance because the question is asking for the gain in PE per second and you know how far the car travels in 1 second (8m/s)
    Hope this gets you into the question
     
  5. Dec 13, 2011 #4
    Does that mean that the answer should be in Watts? Since its J/s?
     
  6. Dec 13, 2011 #5
    Yes.... all the answers will be joules per second....ie watts
     
  7. Dec 13, 2011 #6
    but what exactly does "gain in potential energy per second" mean?
    is it just 8? since that's the velocity
     
  8. Dec 13, 2011 #7
    PE is due to change in VERTICAL height .....mgh......?
    The 8m/s is along the slope.....not vertical
     
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