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Contact Forces with a Massless String

  1. Oct 7, 2008 #1
    1. The problem statement, all variables and given/known data
    Three blocks of equal mass (m = 0.88kg) are placed in a row onto a rough ramp (μ=0.77) whose angle of inclination is 35 (degrees). Each block is connected to the other by a massless string. Suppose you pull upwards on the top block with a force of 34.9N. Answer the following:

    a)Calculate the acceleration of the system.


    2. Relevant equations
    ΣFx

    3. The attempt at a solution
    I have already drawn a free body diagram, co-ordinate plane, and vector diagrams for each of the 3 masses. I also realize that the acceleration of the system holds true for any one of the blocks, that is to say acceleration at m1 equals to acceleration at m2. Furthermore I also realize that all 3 masses are of equal mass.

    My problem in trying to figure out the acceleration of the system in this case, would be isolating the acceleration ("a"), because there are a lot of tensions to take into account in this question.
     
  2. jcsd
  3. Oct 7, 2008 #2

    Hootenanny

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    Sounds like your on the right track. The next step would be to write down Newton's second law for each individual block, so that you end up with a system of three linear equations.
     
  4. Oct 22, 2008 #3
    I found the acceleration (a= 32.2m/s (squared)) for the question but when I got it handed back to me, it said to double check my free body diagrams because there was a mistake in it. This obviously would then make my acceleration calculation incorrect. I have tried to redo my free body diagrams already but would it be possible for someone to post what they would have gotten for the free body diagram(s) so that I could compare diagrams so as to understand this question better?
     
  5. Oct 23, 2008 #4

    Hootenanny

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    Perhaps it would be better if you posted your FBD's are we could point out where you have gone wrong.
     
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