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Homework Help: M1 particle acceleration help

  1. Oct 20, 2007 #1

    Could someone please help me with the following M1 level question?

    A particle rests in limiting equilibrium (that is the particle is on the point of moving and friction has its maximum value) on a plane inclined at 30 degrees to the horizontal. Determine the acceleration with which the particle will slide down the plane when the angle of inclination is increased to 40 degrees.

    I know that limiting equilibrium means that F = miuR.

    Any help would be really appreciated as I am completely stuck over what to do.

    Thank you.

  2. jcsd
  3. Oct 20, 2007 #2


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    Staff Emeritus
    Science Advisor

    The point is that that mass is on an incline.

    Resolve the weight (mg) into components that are parallel and normal to the incline. Use the information at 30° to find [itex]\mu[/itex]. Remember friction is proportional to the normal force and acts opposed the direction of motion (in this case friction points up the incline).

    Then with [itex]\mu[/itex], determine the net force when the incline is tilted to 40°. The component of weight parallel to the incline increases, while the normal force decreases.
    Last edited: Oct 20, 2007
  4. Oct 20, 2007 #3

    Doc Al

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    Staff: Mentor

    I suspect that they want you to assume that the coefficients of static and kinetic friction are the same for this problem. The first step is to solve for that coefficient. Analyze the forces acting on the particle and apply the condition for equilibrium.
  5. Oct 20, 2007 #4
    Thanks so much for your help!

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