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Greater Force= Greater Work; box up ramp

  1. Oct 9, 2006 #1
    Hi, this question seems pretty easy, but I was just wondering if I'm missing anything with my solutions.
    Two ramps, one steeper than the other, are available to move a heavy crate from the ground onto the bed of a truck. In the absence of friction, it takes more force to push the crate up the steeper ramp. Does this mean it also takes more work to raise the crate onto the bed of the truck along the steeper ramp?
    Yes, W=FD, greater F, means great W
    Taking friction into account, which ramp requires less work for pushing the crate on the truck?
    The steeper ramp, as the frictional force will be less. F=cosO*N*u; greater angles means less frictional force
    What is the angle of inclination that minimizes the work, and how is it related to the coefficient of kinetic friction? It seems like the angle that would minimize the work, would be the angle with the least frictional force, but the least frictional force would occur when theta is 90 degrees, or directly vertical, and that doesn't make sense. The coefficient of kinetic friction is not connected to the angle
     
  2. jcsd
  3. Oct 9, 2006 #2

    berkeman

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    I think you got the last 2 correct, but the first one is wrong if there is no friction. Have you learned about how to calculate the change in gravitational potential energy PE yet?
     
  4. Oct 9, 2006 #3

    arildno

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    As for your first question, ask yourself this:
    Is there any difference between the potential energy increase of the crate in the steep case vs. the not-so steep case?

    Arggh, Berkeman is even faster than Lucky Luke..
     
  5. Oct 9, 2006 #4

    arildno

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    "greater angles means less frictional force"

    this is utterly false.

    "Less distance means less work due to frictional force" is the correct expression.
    Do you see the difference?
     
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