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Homework Help: (Non/)Equlibrium and Newton's Laws of Motion

  1. Oct 6, 2007 #1
    This is mainly stumping me because of the absence of any force or mass.

    1. The problem statement, all variables and given/known data

    A crate is sliding down a ramp that is inclined at an angle of 33.6° above the horizontal. The coefficient of kinetic friction between the crate and the ramp surface is 0.485. Find the acceleration of the moving crate.

    [tex]\mu[/tex][tex]_{k}[/tex]= .425
    [tex]\theta[/tex] = 33.6
    g = 9.8m/s[tex]^{2}[/tex]

    2. Relevant equations

    Well, F[tex]_{net}[/tex]x = ma , but there is no mass... I don't know where to go from here. :frown:

    Any help is appreciated. Thanks.
  2. jcsd
  3. Oct 6, 2007 #2
    If you think about the ideal concepts of this type of motion, you can see that mass does not matter. Start to solve the equation as if you had a mass (just use 'm' in place of the unknown quantity) and you'll see it's not as important as you think. If you get stuck in the actual solving, post again with your progress.

  4. Oct 7, 2007 #3
    Ok... I think I'm on the right track. So the net force will be simply

    mgsin[tex]\theta[/tex] - [tex]\mu[/tex]mgcos[tex]\theta[/tex] = ma

    You can divide everything by mass, leaving

    gsin[tex]\theta[/tex] - [tex]\mu[/tex]gcos[tex]\theta[/tex] = a.

    Is this correct?
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