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Two pulleys

  1. Oct 24, 2008 #1
    1. The problem statement, all variables and given/known data
    An object of mass m1 on a frictionless horizontal table is connected to an object of mass m2 through a very light pulley P1 and a light fixed pulley P2 as shown below.
    (a) If a1 and a2 are the accelerations of m1 and m2, respectively, what is the relation between these accelerations? (Use a_2 for a2, m_1 for m1, and m_2 for m2 as appropriate.)
    (b) Express the tensions in the strings in terms of g and the masses m1 and m2. (Use g, m_1 for m1, and m_2 for m2 as appropriate.)
    (c) Express the accelerations a1 and a2 in terms of g and the masses m1 and m2. (Use g, m_1 for m1, and m_2 for m2 as appropriate.)
    http://www.webassign.net/serpop/p4-38.gif
    2. Relevant equations

    F=ma

    3. The attempt at a solution

    First I know that Tension2 = 2Tension1 due to mechanical advantage.
    Therefore,
    Tension 1= m1a1
    Tension 2= m2a2
    if i substitute 2T1 into T2, i get
    2m1a1=m2a2 => a1=m2a2/2m1
    The web assign says it is wrong. Any ideas on how to set this up?
     
  2. jcsd
  3. Oct 24, 2008 #2

    Doc Al

    User Avatar

    Staff: Mentor

    Good.
    Good.
    Not true. (Tension is not the only force acting on m2.)

    Set up Newton's 2nd law for m2.

    You'll also need to figure out how a1 and a2 are related. (They are related, since the pulleys are connected by strings.)
     
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