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Determine acceleration and tensions in this diagram

  1. Oct 4, 2005 #1
    Attached to the following diagram are the following questions:

    (a) determine the acceleration of each object and their directions
    (b) determine the tensions in the two cords

    How would I go about starting/attempting these types of problems?

    I went into college physics, without a strong high school background.

    Thanks, any help would be appreciated.

    Attached Files:

  2. jcsd
  3. Oct 4, 2005 #2
    You want to start off by making a free body diagram for all three masses. You should realize that the tension is not necessarily the same in both pieces of rope.This is easy for the two blocks suspended. The free body diagram of the block on the table will have friction included in it, but you cannot assume a direction for friction, you have to know which way it acts. For example, if you assume the force acts down, but it works out to be negavitve so it acts up, it will work out in the end. This is not true for friction. You HAVE to know which direction it acts.
  4. Oct 5, 2005 #3


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    Hint about friction - it always opposes motion.

    If you assume a direction of motion, then put the friction acting in the opposite direction.

    If you then end up with a negative value for the motion, then your assumption was wrong so reverse the direction/sign for the friction
  5. Oct 10, 2005 #4

    After the Free body diagram is drawn for all three masses, how do i go about calculating tensions and accelerations? is it possible to show me an example of one of the masses (and how you would go about finding the acceleration and tension)? any help would be appreciated at this point. so lost.:uhh:
  6. Oct 10, 2005 #5


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    All three masses are interconnected, so they all have the same acceleration, although in different directions.
    You have drawn the free body diagram, yes ? With all the forces acting on each body.
    Apply newton's 2nd law to each one.
    You should be able to eliminate the two tensions from the simultaneous eqns and be left with acceleration as the only unknown.
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