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Newton's law problem have attempted it

  1. Oct 6, 2005 #1
    Newton's law problem....have attempted it

    http://img128.imageshack.us/img128/2941/asd6rh.jpg

    rope is of negligible mass and no friction.....now this is what i did

    the bc and ab are subscripts for cords between each block

    9.8(10)- Tbc = 10a
    9.8(40)-Tab = 40a
    Tab=30a

    so by substituting i get a =5.6

    then i plug it in to get Tbc.....which gives me 42N.

    but the answer in the book says 36.8N.....dunno what im doing wrong, any ideas?
     
  2. jcsd
  3. Oct 6, 2005 #2

    Tom Mattson

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    This is OK.

    This is not OK.

    You've got the weight of the 40 kg block and the tension pulling upwards, which is good. But Tbc is also acting on the 40 kg block, and you've left that out.

    That's the only mistake I see, so that should fix the problem.
     
  4. Oct 6, 2005 #3

    Tom Mattson

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    And I've deleted your identical thread in the K-12 HW Forum. Please do not post multiple threads for the same topic.
     
  5. Oct 6, 2005 #4
    wow cant believe i didnt think of that....weird
     
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