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Homework Help: Force vector without acceleration

  1. May 15, 2010 #1
    This is just to see if I am totally confused or making sense.

    1. The problem statement, all variables and given/known data
    A truck is pushing up a hill on a 30 degree incline. It has a mass of 45 tons. Find the force vector for the truck.

    2. Relevant equations
    [tex]\vec{F}[/tex] = ||F|| cos[tex]\theta[/tex] i + ||F|| sin[tex]\theta[/tex] j

    3. The attempt at a solution
    [tex]\vec{F}[/tex] = 45 cos30 i + 45 sin30 j
    This is the answer that I assume was wanted, but I don't think that I can say what the force is given only the mass of the truck. After I asked my physics teacher (not the one who gave the quiz), he told me that this is the answer when moving at a constant velocity. If it was stated in the problem that the truck moved at a constant velocity is this correct?
  2. jcsd
  3. May 15, 2010 #2


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    This is a poorly worded problem. Are you working in the USA system of measure? If so, the 45 ton 'mass' of the truck is really its weight....it weighs 90,000 pounds. With this assumption, and the assumptions that the truck is being pushed up the incline at constant velocity, and with a force parallel to the incline, and with no other forces acting on the truck besides its weight, and the x axis is the horizontal axis, and the problem is asking for the pushing force vector, please show how you would arrive at that result for the pushing force vector, in units of pounds. The problem should be more specific in its wording, since there are too many assumptions you have to make.
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