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Dynamics: Moving wedge with mass on it

  1. Feb 19, 2007 #1
    1. The problem statement, all variables and given/known data
    Small block of mass "m" rests on sloping side of triangular block of mass "M" which itself rests on table. Assuming all surfaces are frictionless, determine force "F" that must be applied to "M" so that "m" remains fixed. Wedge incline is "THETA"

    2. Relevant equations

    3. The attempt at a solution
    attached is picture. I don't know where to start, so no attempted solution. The answer is:
    F = (m+M)g*tan(THETA). i don't see why the mass on the wedge would move up the ramp if a force is applied to the left of the wedge.

    where g is acceleration due to gravity

    Attached Files:

    • pic.GIF
      File size:
      907 bytes
  2. jcsd
  3. Feb 19, 2007 #2
    Because of the pseudo force. If a pseudo force F is applied to the wedge, then the acceleration of the wedge+mass system is F/(M+m) and the force on m is mF/(M+m). The projection of that force along the surface of the wedge is equal to the gravitational force acting along the surface of the wedge.
  4. Feb 19, 2007 #3
    k solved it thanks
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