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The drawing shows a large cube (mass = 27 kg) being accelerated across a horizontal frictionless surface by a horizontal force vector P . A small cube (mass = 4.0 kg) is in contact with the front surface of the large cube and will slide downward unless vector P is sufficiently large. The coefficient of static friction between the cubes is 0.71. What is the smallest magnitude that vector P can have in order to keep the small cube from sliding downward?

  • Physics -

    how does a small cube go "downward" if both are on a horizontal surfce? I don't understand the picture painted.

  • Physics -

    | |----|
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    That is what the picture looks like. Hopefully the formatting won't mess up once it is posted. Its like one cube is temporarily glued to the other.

  • Physics -

    Since the formatting messed up...

    Imagine a regular, large cube. A smaller cube is placed on the right hand side of it but it appears as if it is glued to the side of the cube a couple inches above the horizontal surface.

  • Physics -

    ok, I get it. force on the surface keeps it up (actually friction does.)

    The normal force on the front surface of the large cube to the small cube is

    the friction force then holding up the small cube is forcenormal*mu

    and that has to equal smallcubemass*g

    so smallcubemass*g=smallcubemass*a*mu
    or mu=a/g

    Now, what is a? Pushing force= (total mass)a or a=P/totalmass
    so we have...
    solve for P.

  • Physics - the right answer!

  • Physics -

    chuck norris

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