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Two blocks with masses of 4kg and 8kg

  1. Oct 17, 2003 #1
    Two blocks with masses of 4kg and 8kg are connected by a string and slide down a 30 degree inclined plane. The coefficient of kinetic friction between 4kg block and the plane is 0.2; that between 8kg block and the palne is 0.35.
    A) calculate the acceleration of each block.
    b) calculate teh tension in the string
    c) what happens if the positions of the blocks are reversed, so the 4kg block is above teh 8kg block?


    4kg ------- 8kg
    the inclination goes up as it goes right so


    Like that.
    I assumed that the acceleration of block a and b are teh same. can i assume that???? and i soloved it using ma equals w times sin30 - uwcos30 - T
    and Ma = mg sin20 - .25 times mg cos30 - T

    and so on,. I got 2.21 as the accelration. can anybody confirm and tell me how they got it? and for the rest too???
    Last edited by a moderator: Feb 6, 2013
  2. jcsd
  3. Oct 17, 2003 #2

    Chi Meson

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    THe accelerations would be the same in the first scenario, but this is the end result, not the initial assumption.

    THe coefficients of friction are different, so one will drag more than the other.

    THe force of friciton is equal to "mu" times the perpendicular componant of the weight (since that will be the magnitude of the normal force)

    Find the net force that is parallel to the plane for both objects as a system, then divide that force by the total mass.

    I got 0.718 m/s^2 as the acceleration
    Last edited: Oct 17, 2003
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