Dismiss Notice
Join Physics Forums Today!
The friendliest, high quality science and math community on the planet! Everyone who loves science is here!

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
    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


    User Avatar
    Science Advisor
    Homework Helper
    Gold Member

    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
Share this great discussion with others via Reddit, Google+, Twitter, or Facebook