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2 blocks, each on an inclined plane

  1. Jan 18, 2010 #1
    1. The problem statement, all variables and given/known data
    Two 2kg blocks are joined by a massless cord and pulley, ignoring friction, determine each block's acceleration using a free body diagram for each.

    Picture for visual aid: http://img27.imageshack.us/img27/2653/86460048.png [Broken]
    or a link: http://img27.imageshack.us/img27/2653/86460048.png [Broken]


    3. The attempt at a solution
    I did the free body diagrams and solved for the tension on the string to try to equate the two sides

    for the first block i got: T - mgsin30 = ma(1) so T = ma(1) + mgsin30
    for the second block i got: mgsin60 - T = ma(2) so T = mgsin60 - ma(2)

    The problem is the fact that i have two variables that i am solving for. I can't figure it out
     
    Last edited by a moderator: May 4, 2017
  2. jcsd
  3. Jan 18, 2010 #2

    tiny-tim

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    Welcome to PF!

    Hi RonakPat! Welcome to PF! :smile:

    You're missing the obvious …

    the length of the string is constant, so a1 + a2 = 0. :wink:

    (some people call that a geometric constraint)
     
  4. Jan 18, 2010 #3
    Re: Welcome to PF!

    So should I still set the two things equal then substitute one of the accelerations(a2) out to find the other(a1) then use what you gave me to find the other(a2)?
     
  5. Jan 18, 2010 #4

    tiny-tim

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    Equal and opposite, yes. :smile:
     
  6. Jan 18, 2010 #5
    Well i solved it and it came out to be 1.79m/s2. Does it matter which of them has the negative acceleration or do both have equal positive accelerations?
     
  7. Jan 18, 2010 #6

    tiny-tim

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    hmm … well, you'd better say that one goes upward with acceleration 1.79m/s2, and the other goes downward …

    you'll have to make it clear you know which way they're going! :wink: :biggrin:
     
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