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Mechanics help !

  1. Nov 24, 2011 #1
    Mechanics help :(!

    Two blocks are connected by a cord which passes over a frictionless pulley at D.
    Block A has a mass of 40 kg and block B a
    mass of 120 kg. A rests on a horizontal
    surface, while B rests on a ramp with the slope
    shown. B is initially in a position 3 m from the
    stop C as shown. The coefficient of kinetic
    friction between the blocks and the surface
    beneath is μK = 0.20 for both A and B.

    (a) Find the acceleration of the two blocks and
    the tension T in the cord, assuming that the
    blocks just begin to move at time t = 0.
  2. jcsd
  3. Nov 24, 2011 #2
    Re: Mechanics help :(!

  4. Nov 24, 2011 #3
  5. Nov 24, 2011 #4
    Re: Mechanics help :(!

    First we draw the FBD for mass A and for mass B.

    How many forces act on each?
  6. Nov 24, 2011 #5
    Re: Mechanics help :(!

    on mass 1 we have forcetension - forcefriction + m*g = ma
    mass2 -frocetension-Forcefriction2+(m*g)sin theta= m2a

    the thing thats confusing me is if we could have assumed that the aceleration of B is same as acceleration of a before it hits the barrier in the diagram
  7. Nov 25, 2011 #6
    Re: Mechanics help :(!

    To avoid confusion, instead of mass 1 let us call it mass A as in diagram.

    Re 1st equation: I do not know why you have m*g.

    Until mass B hits the barrier at C we HAVE TO assume that the acceleration of B is the same (in magnitude) as that of A because otherwise the string either snaps or becomes slack and so there would not be any tension at all!
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