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Homework Help: 2 block tension problem

  1. Oct 6, 2006 #1


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    2 block tension problem....

    I dont have a good picture to put up, but this is what is given in my book:

    A force of 12 N is exerted on a 1.0 kg block. Both the force and the block are both on a plane that is at a 37 degree angle with the ground. A rope connects this block to another block (this time 3.0 kg) that is on the flat ground (to the left of the incline according to the picture) by means of a pulley.

    please excuse the horrible animation.

    I have to calculate (assuming frictionless and massless pulley and plane) the force of tension in the connecting cord. I tried using F - mgsin37 = ma for the 1 kg block, but this doesnt give me the answer that is in the back of the book (which is 4.6 N). I am really not sure how to derive tension, it is my biggest weakness in dynamics, at least when the pully is not working with ropes which are at right angles with each other.
  2. jcsd
  3. Oct 6, 2006 #2
    you dont have to take into consideration the angle at which the force is exerted, since the mass and the force lie on the same plane.
  4. Oct 6, 2006 #3


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    Consider the forces acting on each of the blocks. The block on the ramp has 3 forces parallel to the plane: the mgsin37 you have identified, the applied 12N and the tension in the rope. These forces result in an acceleration yet to be determined. The block on the flat ground has only the tension acting horizonatally, resulting in an acceleration. The blocks have two things in common: the tension in the rope and the magnitude of the acceleration. Both of these can be found by applying F = ma to each block and solving the two resulting equations.
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