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Homework Help: Acceleration of block down an incline

  1. Nov 26, 2008 #1
    1. The problem statement, all variables and given/known data
    06_38.gif

    Find the acceleration of block A when moving downward

    Theta=40 degrees
    A=103N
    B=31N
    Static coefficient = 0.56
    Kinetic coefficient = 0.25

    2. Relevant equations

    F=ma
    Normal Force * Kinetic coefficient = Friction Force

    3. The attempt at a solution

    From 103/9.8 I get a mass of ~10.5

    Breaking 103 into components, 103sin40 and 103cos40, the first being perpendicular and the second being along the plane

    103sin40*0.25=Friction Force

    Tension is 31, so the sum of forces is:

    (31+103sin40*0.25)-103cos40 = Fnet

    Fnet/10.5 = Acceleration of A

    is this correct?

    Thanks!
     
    Last edited: Nov 26, 2008
  2. jcsd
  3. Nov 26, 2008 #2
    you have mixed up the normal force and the force going down the ramp

    mgcos40 would be the FN ; use this to find the frictional force
    mgsin40 would be the force with which it accelerates down the ramp

    try writing some net force equations ; those would help :]
     
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