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Homework Help: Centrepetal Force & Inclined Plane

  1. Oct 8, 2008 #1
    1. The problem statement, all variables and given/known data
    I Have two questions one of them i just cant start it, I don't understand what it is I'm supposed to set up or how.

    A Block is shoved up a 22 degree slope with an initial velocity of 1.4 m/s the coefficient of friction is .70 how far up the slope will the block make it? once stopped will it slide back down?

    2. Relevant equations
    Fg = mg
    Fa = ma
    4 kinematic equations?

    3. The attempt at a solution

    well i drew out my FBD and i have tried

    Fg(incline) = mgSin(22)
    Fn = mgCos(22)
    Ffr = (Mu)mgCos(22)

    And from there... I'm stuck, i do however have no idea how i can solve this i tried doing

    m(-9.81)(Sin(22)) = -(.70)(-9.81)(Cos(22))m

    but mass cancels and your ending up with no unit's which I Am assuming is incorrect, i just don't know what equations i need to set up for this problem :(

    1. The problem statement, all variables and given/known data
    Problem 2
    A washing machine’s drum is rotating rapidly (about its vertical axis). A wet sock is stuck on the inside, halfway up
    the drum. The drum begins to slow its rotation. How many rotations per second is the drum making when the sock falls to
    the bottom of the drum? The coefficient of friction between the sock and the drum is 0.13, and the drum radius is 0.35 m.

    2. Relevant equations

    ac = v^2/r

    3. The attempt at a solution

    Circum. = 2.166
    all i really want to know is am i correct in saying


    if not, i will reattempt, at least using that my mass is not needed :)
  2. jcsd
  3. Oct 8, 2008 #2

    Doc Al

    User Avatar

    Staff: Mentor

    Problem 1:
    Apply Newton's 2nd law to solve for the acceleration: ΣF = ma.

    Problem 2:
    That is a correct statement of the condition for the sock to fall.
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