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Homework Help: Force and Motion with two unknows

  1. Oct 15, 2008 #1
    Body A in Fig. 6-36 weighs 100 N, and body B weighs 77 N. The coefficients of friction between A and the incline are μs = 0.52 and μk = 0.28. Angle θ is 31°. 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?
    http://edugen.wiley.com/edugen/courses/crs1650/art/qb/qu/c06/fig06_34.gif

    =S m stuck @ -FT + mgsintheta = ma and i am stuck with two unknowns.. Tension and acceleration
     
    Last edited: Oct 16, 2008
  2. jcsd
  3. Oct 16, 2008 #2

    tiny-tim

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    Welcome to PF!

    Hi ankitp3! Welcome to PF! :smile:

    Yes, you do have two unknowns.. tension and acceleration …

    but you also have two equations, one for body A and one for body B. :wink:
     
  4. Oct 16, 2008 #3
    Re: Welcome to PF!

    still having hard time solving this problem :S
     
  5. Oct 17, 2008 #4

    tiny-tim

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    ok, show us your two equations, and we'll see what we can do … :smile:
     
  6. Oct 17, 2008 #5
    FK + mgsingtheta - FT = m1ax (block A)

    Ft - Fg = m2gy (block b)

    ukmgcostheta - mgsintheta - FT = m1ax

    Ft - (wB) = (wB/9.8)a

    ukmgcostheta + mgsintheta - Ft (< sub in Ft from the last equation)
     
  7. Oct 17, 2008 #6

    tiny-tim

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    Sorry … I've stared at this for several minutes and I can't follow it. :confused:

    Can you put the numbers in? :smile:
     
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