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Homework Help: Need help with tension acceleration problem

  1. Oct 6, 2005 #1
    Block sitting on table is 442 N , there is a pulley at the end of table with another 185 N box hanging from a rope that goes through the pulley and attaches to the first box on table. The pulley is massless , I need help finding the acceleration , and the tension....It says ignore all frictional affects and assume the pulley is massless?
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  3. Oct 6, 2005 #2

    Andrew Mason

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    What do you mean by the first block being 442 N? Does this mean mg = 442 N?

  4. Oct 6, 2005 #3
    It just says the (weight) of the block on the table is 422 (N)ewtons
  5. Oct 6, 2005 #4

    Physics Monkey

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    All you need to do is apply Newton's second law to each block and realize that the blocks will accelerate together. You know the masses of the blocks in terms of their weight and the gravitational acceleration. What are the forces acting on each block?
  6. Oct 7, 2005 #5
    how can they be accelerating

    How can they be accelerating if the block on top has more force applied to it than the block hang off the table? wouldn't they just sit there? How do you apply newtons 2nd law to find the tension of the rope. Box 2 is offsetting box one isn't it?
  7. Oct 7, 2005 #6
    please help

    I know I need to apply newtons 2nd law to the boxes but how do i do that?
  8. Oct 7, 2005 #7

    Physics Monkey

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    Well, you should start by identifying all the forces acting on each box. That's always how you apply Newton's 2nd law.
  9. Oct 7, 2005 #8


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    There's a caveat (which is the fun of this problem) though:
    Don't assume that there is simply 185 N pulling on the bloc on the table ! Call the force transmitted through the rope (= the tension) F and work on from there.

  10. Oct 7, 2005 #9


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    A massless tense rope pulls inward at each end
    with Forces that have same absolute value.

    Horizontal motion is independent of vertical motion,
    (ie, the 442 N is opposed by the F_N by table).
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