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Homework Help: Raising a platofrm at an angle

  1. Sep 24, 2010 #1
    1. The problem statement, all variables and given/known data
    A 33.5 kg person stands on a 67 kg platform.
    He pulls on the rope that is attached to the
    platform via the frictionless lower-right pul-
    ley. He pulls the rope at an angle of 35◦ to the
    horizontal, as shown in the figure below.
    Assume: g = 9.8 m/s2 . Ignore friction.
    The platform remains level.
    [PLAIN]http://img201.imageshack.us/img201/5122/010011.png [Broken]

    (a) If he pulls the platform up at a steady rate,
    how much force is he pulling on the rope?

    (b)In Part 1 we assumed that the platform re-
    mains level. This is a bad assumption.
    However, if the man were pulling straight
    up on the rope, the forces will be balanced
    and the platform should remain level.
    1. This is a good assumption.
    2. Cannot be determined.
    3. This also is a bad assumption.

    2. Relevant equations
    Sum of Fy= T-Mg=0=> Mg=N, where M=m1+m2
    Sum of Fy= N-Mg+Fsintheta=Ma
    Sum of Fx=Fcostheta=0

    3. The attempt at a solution
    So I know T7=T6, does T7 also equal T2?
    Does T5= T7+T6?
    Does T3=T1+T2?

    What equation can I use to calculate T1?
    Last edited by a moderator: May 4, 2017
  2. jcsd
  3. Sep 24, 2010 #2

    Chi Meson

    User Avatar
    Science Advisor
    Homework Helper

    What are T5 and T3 supposed to be? The tension where the pulleys are fixed to the ceiling?

    Anyway, frictionless pulleys will not change the tension at any point in the single rope. So T1, T2, T4, T6, and T7 are all equal. But when examining net forces, you look at each of these "Ts" when finding the net force on an object. So haw many of these tensions are supporting the platform?

    How many of these te
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