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Homework Help: Friction: Blocks and Plane

  1. Oct 2, 2009 #1
    1. The problem statement, all variables and given/known data

    Masses m1 and m2 are attached via a light string and pulley on an inclined plane as shown above. m1 has a value of 12 kg and moves down the plane at a constant velocity of 0.9 m/sec. The plane is tilted upwards at an angle of Θ = 26 °. The coefficient of static friction between m1 and the plane is μs = 0.24 and the coefficient of kinetic friction is μk = 0.19.

    https://wug-s.physics.uiuc.edu/cgi/courses/shell/common/showme.pl?cc/DuPage/phys2111/fall/homework/Ch-06-Forces/friction_block_plane/plane_blocks.gif [Broken]

    What is the mass of m2?

    2. Relevant equations

    F = ma
    f = uk(m1)g

    3. The attempt at a solution

    y1: m1sin(theta) - T - f = m1a
    x1: N - mgcos(theta) = m1a

    y2: T -m2g = m2a

    Plugging in the numbers in to y1 and then I set it equal to T. I then put that equation into y2 and I got 8.5kg for m2, and apparently this is incorrect. Any ideas?
    Is my free body diagram correct? Thanks!

    Attached Files:

    Last edited by a moderator: May 4, 2017
  2. jcsd
  3. Oct 2, 2009 #2


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    Gold Member

    You forgot the "g" in m1sin(theta)
    The acceleration in a direction perpendicular to the plane is zero because, as it moves, the block does not jump off or sink into the plane. Use the correct N to find the force of friction f.
    This is OK.
  4. Oct 2, 2009 #3


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    Missing a factor of g in the first term. And of course a=0 so the right side is zero.
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