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Some help please on a Question

  1. Sep 13, 2007 #1
    1. The problem statement, all variables and given/known data
    This has had me puzzled for a few hours now,
    Its about forces acting down a plane.

    Q. A car of a mass (m) is travelling with a constant velocity up a hill at an angle (any angle - theta ) to the horizontal as indicated


    If F is the resultant force acting on the car, the effective engine force needed to maintain this consant velocity must be
    A = mgcos(theta) + F
    B = mgcos(theta) - F
    C = mgsin(theta) + F
    D = mgsin(theta) - F
    E = mg + Fsin(theta)

    Any help will be apprieciated

    My work

    I tried making up values for the equations. It worked but it didnt really match the equations matched in the answer.
    Fh = fcos(theta) Horizontal Force
    Fv = fsin(theta) Vertical Force

    As its horizontal I have igonred the answers with sin. But I somehow dont know why it either has to be plus or minus F. Would that not equal an unbalanced force.
    Last edited: Sep 13, 2007
  2. jcsd
  3. Sep 13, 2007 #2

    Doc Al

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    Staff: Mentor

    What is the meaning of "Resultant Force"? Resultant of what? (It can't mean net force, since the car is moving at constant velocity.)
  4. Sep 13, 2007 #3
    the result of all the friction acting on it

    Basically just the friction
  5. Sep 13, 2007 #4


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    Homework Helper

    what is the net force acting on the car (not the resultant force, but the net force)?
  6. Sep 13, 2007 #5
    Net force ?

    The question dosnt give any values. Its to try and find the correct formula that would work.
    All the info Im given is shown there
  7. Sep 13, 2007 #6


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    Homework Helper

    hint: the car is moving at a constant velocity... this information should let you know what the net force acting on the car is.
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