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Homework Help: Force problem

  1. Jul 15, 2007 #1
    1. The problem statement, all variables and given/known data

    A block with a weight of 2.9 N is at rest on a horizontal surface. A 1.3 N upward force is applied to the block by means of attached vertical string.
    (a) What is the magnitude of the force of the block on the horizontal surface?

    2. Relevant equations

    I'm not sure really..

    3. The attempt at a solution

    I have tried solving this from several different angles. I thought to use F=2.9Nx9.81-1.3, but I believe that is incorrect.
  2. jcsd
  3. Jul 15, 2007 #2


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    This looks right except I don't think you want to multiply the 2.9N force with a 9.81, which I believe would be the acceleration of the block towards the earth in [tex]ms^{-2}[/tex]. Force cross acceleration is not something people are usually interested in, especially if they are in the same direction, because it equals zero.

    Imagine the block pushing the surface with 2.9N force and an opposing force of 1.3N acts in the opposite direction to cancel out 1.3N of the original force acting on the surface. Hope this helped.
  4. Jul 15, 2007 #3
    Thank you!
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