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Applied force on two blocks on a horizontal frictional plane

  1. Oct 13, 2009 #1
    1. The problem statement, all variables and given/known data
    Two blocks connected by a string are pulled
    across a rough horizontal surface by a force
    applied to one of the blocks.
    The acceleration of gravity is 9.8 m/s2 .
    1st block = 2 kg
    2nd block = 8 kg
    Force on second block at 52◦
    μ = 0.29

    [ 2kg ]-------[ 8kg ]/ 52 degrees

    If each block has an acceleration of 1.6 m/s2
    to the right, what is the magnitude of the
    applied force? Answer in units of N.

    2. Relevant equations

    3. The attempt at a solution

    What I got was 72.15 N but I got it wrong and I have no idea what I did wrong
    Last edited: Oct 13, 2009
  2. jcsd
  3. Oct 13, 2009 #2
    Draw a fbd and sum the forces for each block in the x and y.
  4. Oct 13, 2009 #3
    what do i use for the force against friction for the block being pulled?
  5. Oct 13, 2009 #4
    You need to find an expression for the normal force. In the y direction the force of gravity acts downward, the normal force acts upward, and the applied force acts upward.
  6. Oct 13, 2009 #5
    ok for the 8kg block i got 39.30N the problem that i am having for the 2kg block is that i do not no what Force I am solving for that is pulling the block is it Fcos60 like the previous one or is it the tension of the string
  7. Oct 13, 2009 #6
    The tension in the string is pulling the second block.
  8. Oct 13, 2009 #7
    would you find that simply by multiplying mass times acceleration of the 2kg block?
    Last edited: Oct 13, 2009
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