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Rectangular box tips over (or not)

  1. Jan 31, 2012 #1
    1. The problem statement, all variables and given/known data
    A uniform rectangular wood block of mass M, with length b and height a, rests on an incline as shown. The incline and the wood block have a coefficient of static friction, μs. The incline is moved upwards from an angle of zero through an angle θ. At some critical angle the block will either tip over or slip down the plane. Determine the relationship between a, b, and μs such that the block will tip over (and not slip) at the critical angle. The box is rectangular, and a ̸= b.

    2. Relevant equations


    3. The attempt at a solution

    I'm assuming this has to do with torque. There is the normal force doing torque (right?) but that's all I could see. Perhaps gravity also does torque but I'm having trouble seeing how much the radius in the torque formula would be and where does the static friction coefficient come in?
  2. jcsd
  3. Feb 1, 2012 #2


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    Homework Helper

    Hi usamo,

    Start with a picture, showing all the forces and torques.

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