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Equlibrium problem

  1. May 10, 2009 #1
    Equilibrium problem

    1. The problem statement, all variables and given/known data
    http://www.deviantpics.com/image.php?id=5029_4A04401C

    Mass m is atached to the wall with a light string and set on a trolley with an inclined plane.
    The string is parallel with the plane. Let's say that there is no friction at all.
    Determine intensity of the horizontal force which has to act upon the trolley so that the system stays motionless.


    2. The attempt at a solution

    Tsin(alpha)=G
    Tcos(alpha)=F

    F=mg/tg(alpha)

    But I'm not sure if this is correct. If we let alpha be 0° than force F would have to be infinite. Also this would mean that tension T is greater than G and that seems odd too.Can you please tell we what am I doing wrong?


    Thanks
     
    Last edited: May 10, 2009
  2. jcsd
  3. May 10, 2009 #2

    diazona

    User Avatar
    Homework Helper

    In the picture above you've considered the trolley and the block as one object, but that's not really valid because they are not rigidly attached to each other. Try drawing a separate free-body diagram for each, and taking into account the normal force that the trolley exerts on the block (and vice-versa). I get what seems like a more reasonable answer doing it that way.
     
  4. May 10, 2009 #3
    OK this is what I get:

    http://www.deviantpics.com/image.php?id=CDD1_4A071DF0

    Is this any good?
    In this case T would be mg*sin(a).
     
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