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Homework Help: A force problem that seems easy but hard

  1. Nov 2, 2006 #1
    A 2.00-kg aluminum block and a 6.00-kg copper block are connected by a light string over a frictionless pulley. The two blocks are allowed to move on a fixed steel block wedge (of angle 30.0) as shown in Figure P4.53. Making use of Table 4.2, determine (a) the acceleration of the two blocks and (b) the tension in the string.

    My work so far:
    For the aluminum block - I got T = 2a, which I cannot solve
    For the copper block - I got Tx-58.8sin(30) = 6a - this is for x direction
    Ny-58.8cos(30) = 6a - this is for y direction

    58.8 is the weight force, which comes from 6*9.8 = 58.8N
    T = tension force
    N = Normal force

    All the equations won't get me to solve for acceleration for either blocks


    If you cannot see the attachment, you may click http://students.washington.edu/cy1126/P4.53.jpg" [Broken]

    Attached Files:

    Last edited by a moderator: May 2, 2017
  2. jcsd
  3. Nov 3, 2006 #2
    You don't need an x for the direction of T for the copper block since you are resolving it along the surface of the plane. Once you get this, its semple simultaneous equations.
  4. Nov 3, 2006 #3
    I see what you are saying, but for the copper block, I defined the x axis to be the the ramp. Therefore, the coordinate diagram is a slanted one, not a standard one. As a result, you need Tx
  5. Nov 3, 2006 #4
    Neither block is accelerating in the y as you have defined it. Tension is purely in the x. You then get 2 equations with 2 unknowns because the tensions and accelerations are equal
  6. Nov 4, 2006 #5
    If I get what you mean, you should not do that becaus you would need to take into account the normal force.
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