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Homework Help: Moving wedge, conceptual problem

  1. Dec 5, 2011 #1
    1. The problem statement, all variables and given/known data

    For general values of m, M, theta, mu (coefficient of static fric) find the minimum force you need to apply to the wedge so that it just begins moving up the slope.


    (little m represents mass on wedge, M is mass of wedge.)


    2. Relevant equations

    I know the idea is to use the forces on the small block to find its acceleration then multiply this by the mass of the wedge and the mass of the block (I do, infact have the solution, I just don't understand it) but I am having trouble understanding how the force applied to the wedge causes the block to move upward, according to the given force diagram (below) none of the forces (normal, gravity, friction) have components in the upward direction of the slope. If anyone could explain this to me I would greatly appreciate it.


    3. The attempt at a solution

    See above.
  2. jcsd
  3. Dec 5, 2011 #2
    As an object(in this case the wedge), moves under the influence of a force, it accelerates, making it, a non-inertial reference frame.
    Therefore, in the frame of reference of the box, it[the box] will experience an inertial force("fictitious force"), in the direction opposite to the application of the force on the wedge, valued at: [itex] F' = -ma [/itex], Where a is the acceleration of the wedge.
    I hope that helps,
  4. Dec 6, 2011 #3
    Thanks, I've been struggling with this problem for quite a while.
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