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Pulley problem using 2nd Law of motion

  1. Dec 6, 2005 #1

    KD

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    This is hard to explain without having a picture, but there is a 1 kg hanging off the table. And a string is connected from that to a 10kg weight. From that weight on the other side, a 5kg weight hangs off the table. They system is moving to the left at 2 m/s. Do I have to compensate for that in any of my calculations because I believe it accelerates to the right b/c of the larger weight.
     
    Last edited: Dec 6, 2005
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  3. Dec 6, 2005 #2

    Astronuc

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    Staff: Mentor

    OK, is the speed constant at 2 m/s? If so then the net force is zero, because there is no acceleration.

    Presumably the 5 kg weight is falling, the 1 kg weight is rising, and the 10 kg weight is resisting the motion with friction.

    Are you trying to find the dynamic or kinetic coefficient of friction for the 10 kg mass, or tensions in the strings?
     
  4. Dec 6, 2005 #3

    KD

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    Sorry, I forgot to include those parts in the problems.
    Disregard all friction. It doesn't indicate a constant velocity so I am assuming there is an acceleration.

    To find the acceleration I used a system consisting of T1-W1=m1a; T2-W2=-m2a; and T2-T1=m3a. This is a probably a dumb question, but the system can still acclerate to the right even though it is moving the left, right?

    What I have left to find in this problem is when the system stops moving to the left and how far left. I'm pretty sure I can figure that out using simple kinematics.
     
  5. Dec 6, 2005 #4

    Astronuc

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    I have to pop out for little while, but I shall return.

    Meanwhile, please elaborate on the which weight is on which side.

    If the 2 m/s is an instantaneous velocity, then yes there could be an acceleration involved. Not knowing the initial conditions though, the system could be decelerating or accelerating, depending on the net force.

    I presume then 10 kg mass slides across the table?
     
  6. Dec 6, 2005 #5

    KD

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    1 kg is on the left, 10kg is on the table, and 5 kg is on the right. It's really a simple problem, you don't have to consider much else (like friction or anything). I'm using the 2m/s as an inital velocity. The problem states "Assume the table to be sufficiently long for the motion to occur without collision with the pulleys."
    I got the acceleration to be 2.45m/s2 to the right but I didn't know if that could be, if the movement was to the left.
     
  7. Dec 6, 2005 #6
    yes, that's right.
     
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