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Homework Help: Lifting a prism; coefficient of friction

  1. May 29, 2012 #1
    1. The problem statement, all variables and given/known data
    A prism has a mass of m = 80 g, and you wish to lift it, touching
    the upper two faces only. If the coecient of friction between the prism’s surface and
    your skin is  = 0:4, what is the minimum force that must be applied to each face?

    2. Relevant equations

    3. The attempt at a solution
    I drew the forces perpendicular to the two surfaces. I don't really know how to resolve them, and how F=μR comes into it.
  2. jcsd
  3. May 30, 2012 #2
    The question seems incomplete without mentioning what kind of prism it is...You cannot resolve the forces to anything useful. if you don't know the prism angle.
  4. May 30, 2012 #3
    We need a net force equal the weight of the prism, passing thru the centre of mass.
    This net force is equal to the resultant of 2 forces, each from each finger.
    The force from each finger is equal or less than maximum static friction between finder and prism.
    The static friction is equal μN where N equal to force applied if it is applied perpendicularly to the plane of the prism.
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