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Beginner's mechanics problem

  1. Feb 23, 2008 #1
    Hello.
    I have the attached problem.
    The body whose mass is m doesn't move relative to the body M. Them both are affected only by gravity.
    I need to find the angle phi.

    Can anyone please help me?

    http://img135.imageshack.us/img135/4690/1113169793tx6.gif

    Thank you.
     
  2. jcsd
  3. Feb 23, 2008 #2

    Doc Al

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    Staff: Mentor

    Show us what you've done so far and point out where you got stuck.

    Hint: What's the motion of that contraption along the incline?
     
  4. Feb 23, 2008 #3
    well, I tried to draw the forces on the little mass m, and I know the whole contraption is under a force (mgsin(alpha)), and I got to the point that on the little mass, I have the tension and the mg force and a d'elambert force to the left.
    Im kinda stuck on doing that on the whole thing. I don't really know how to relate to the little mass in reference with the M mass, ie - I want to write the motion equations from the accelerating contraptions' POV, but then I don't know how to take the m mass's forces (should I take it as another force, ie mg+Mg=mgsinalpha, or not...).
     
  5. Feb 23, 2008 #4

    Doc Al

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    Staff: Mentor

    D'alembertian forces? Let's have none of that crazy talk! :wink:

    What's the acceleration of the contraption (and thus mass m)? Analyze forces parallel and perpendicular to the incline and apply good old Newton.
     
  6. Feb 23, 2008 #5
    Thanks.
    I think I got it... I'll try it and see how it turns out
    :)
     
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