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Homework Help: Three boxes on different inclines

  1. Feb 25, 2014 #1
    1. The problem statement, all variables and given/known data
    There are three boxes, box B weighs 2.0kg, and is sitting on a flat surface. To the left is box A, tied to box B. Box A weighs 8.0kg and is sitting on an incline 110 degrees from the horizontal (or 70 depending on the location of the measurement). To the right of box B is box C, sitting on an angle 130* from the horizontal, tied to box B. It weighs 9.0kg. All ropes are supported by pulleys.
    a)assuming no friction, calculate acceleration of the system
    b) calculate coefficient of static friction to remain motionless
    c) coefficient of kinetic friction is 0.050, calculate acceleration and tension in both strings

    2. Relevant equations
    fnet = ma

    3. The attempt at a solution
    I managed to get an acceleration of 1.57m/s to the right, but I feel like it's wrong, I can't seem to get the components of gravity to work out right, I think I'm doing something wrong there.
    I haven't got to B or C because I don't want to go through the entire thing with incorrect numbers.
  2. jcsd
  3. Feb 25, 2014 #2
    Update : turns out I had cosine and sine reversed so my components were in the wrong direction, I got an acceleration of 0.57 m/s/s which is much more reasonable.
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