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Homework Help: Pully problem

  1. Oct 28, 2007 #1
    1. The problem statement, all variables and given/known data
    Two masses, located on a frictionless, horizontal surface, are tied together by a string. The masses are attached to a second string which passes over a pulley and has a third weight attached which hangs vertically. Find the acceleration of the system and the tensions of the horizontal strings. (uk: .15) Mass 1= 10 kg attached to Mass 2: 20kg attached to mass 3 (vertical): 15kg.

    2. Relevant equations

    a= (m2-ukm1)g/ (m1+m2)
    a= (m2-m1)g/ (m1+m2)

    3. The attempt at a solution

    a= (15-.15*30)9.8/ 45
    a= 2.3 m/s2

    Please help ASAP!!!!
  2. jcsd
  3. Oct 28, 2007 #2
    what do your force-body diagrams look like?

    also, you need 3 FBD since you're dealing with 3 masses.
  4. Oct 28, 2007 #3
    Hi! It's in the attachment.


    Attached Files:

    • fbd.doc
      File size:
      23.5 KB
  5. Oct 28, 2007 #4
    your attachment will take too long to be approved, you're better off just linking it
  6. Oct 28, 2007 #5
    I don't really know how to do that! But the vertical one is with tension going up and weight going down, the first weight is normal force going up and weight going down, and the second horizontal weight is normal force going up and weight going down. The tensions are up for the vertical weight and to the left for the two horizontal weights.
  7. Oct 28, 2007 #6
    is this what your FBD should look like?

    http://img89.imageshack.us/img89/5333/probnj2.jpg [Broken]

    are they both attached to the string or just the lower box?
    Last edited by a moderator: May 3, 2017
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