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Inclined place friction problem

  1. Jun 5, 2012 #1
    1. The problem statement, all variables and given/known data

    Body A in Fig. 6-33 weighs 96 N, and body B weighs 88 N. The coefficients of friction between A and the incline are μs = 0.54 and μk = 0.24. Angle θ is 42°. Let the positive direction of an x axis be down the slope. What is the acceleration of A if A is initially (a) at rest, (b) moving up the incline, and (c) moving down the incline

    2. Relevant equations

    fs=usFn
    Fk=ukFN
    a=v^2/R

    3. The attempt at a solution
    I am so confused on this problem i dot even know where to start but I know part a is 0!
     
  2. jcsd
  3. Jun 5, 2012 #2
    Here is the diagram
     

    Attached Files:

  4. Jun 5, 2012 #3
    Let's start with by drawing a free-body diagram for each mass.
    Mass A has a force downward to center of earth equal to its weight, the string that pulls it and third the friction that will appose the motion of the mass.
    Mass B has 2 forces acting on it. Its weight and the string that pull up.

    Remember if there is the net forces(ƩF≠0) on each mass then there's acceleration as in Newton's First Law.
    Fnet=ma
     
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