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Static force equilibrium problem involving simply pully syst

  1. Jul 3, 2015 #1
    1. The problem statement, all variables and given/known data
    A former student of mechanics wishes to weigh himself but has access only to a scale A with capacity limited to 120 lbs and a small 20-lb spring dynamometer B. With the rig shown he discovers that when he exerts a pull on the rope so that B registers 19 lb, the scale A reads 96 lb. What is his correct weight?

    http://edugen.wileyplus.com/edugen/courses/crs7925/art/qb/EAT_1314936802947_0_5416955130664096.jpg


    2. Relevant equations
    ΣF=0

    3. The attempt at a solution
    20150703_115323_zpsnkhqktuf.jpg
     
  2. jcsd
  3. Jul 3, 2015 #2
    Take more care to only add all the forces acting on an object. If a weight is only acting through a tension, then you add only the tension not the weight too.
     
  4. Jul 3, 2015 #3
    yes of course. ΣFy= -19-96+4TB-TA=0 thanks Dr
     
  5. Jul 3, 2015 #4

    SammyS

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    Unfortunately, we can't open that link from Wiley without a username/password.
     
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