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2 weights on a pully, show formula

  1. Sep 30, 2009 #1
    1. The problem statement, all variables and given/known data

    The apparatus (see link to image) is used to measure the free fall acceleration g by measuring the acceleration of the two blocks connected by a string over a pulley. Asume a massless, frictionless pulley and a massless string.
    http://img3.imageshack.us/img3/3459/phys.th.png [Broken]
    a) draw a free body diagram of each block
    http://img16.imageshack.us/img16/3523/diagrams.th.png [Broken]
    b)use the free body diagrams and Newton's laws to show that the magnitude of acceleration of either block and tension in string are a=(m1-2)/(m1+2)
    c)do these expressions give reasonable results if m1=m2 in the limit that m1 >> m2 and in the limit that m1 << m2 ? Explain

    2. Relevant equations

    Fnet=ma
    Fg=mg


    3. The attempt at a solution
    F=ma
    T_1=-T_2
    T_2=(m_2)g
    T_1=(m_1)g
    =>m_1(g)=-m_2(g)
     
    Last edited by a moderator: May 4, 2017
  2. jcsd
  3. Sep 30, 2009 #2

    rock.freak667

    User Avatar
    Homework Helper

    Assume block one moves downwards, so the resultant force on m1 is

    m1a=mg-T

    So what is the resultant force on m2?

    Now you have two equations in T and a, you can now eliminate T.
     
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