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What did I do wrong? (Newton's Second Law)

  1. Oct 19, 2014 #1
    1. The problem statement, all variables and given/known data
    (This is a problem I made up, so if the problem is with the problem, let me know.)
    A 500N ball is being pushed down a carpeted decline of 24° to the horizontal. It starts from 1 m/s and ends the 20 foot (6.1 m) decline at 32 m/s. What is the coefficient and force of kinetic friction and applied force?

    2. Relevant equations
    I used:
    Fg = mag, F = ma, a = μkg, and vi = √(vf2 - (2ad)).

    3. The attempt at a solution
    Fg = mag
    50N = m(9.81)
    m = 5kg
    vi = √(vf2 - (2ad))
    1 = √(322 - 2a(6.1))
    1 = √(1024 - 12.2a)
    1 = √(1011.8a)
    1 = 38√(a)
    1/38 = √(a)
    .022 = a
    a = .0004 m/s2
    F = ma
    F = 5*.0004
    F = .002N
    a = μkg
    .0004 = μk(9.81)
    μk = .000040775
     
  2. jcsd
  3. Oct 20, 2014 #2

    CWatters

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    Does that value for "a" seem reasonable to you?

    I know the equation as...

    vf2 = vi2 + 2ad

    2ad = vf2 - vi2

    a = (vf2 - vi2)/2d

    a = (1024 - 1) / (2*6.1)
    = 84m/s2
     
  4. Oct 20, 2014 #3

    CWatters

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    PS: It may not be your only error. I haven't checked.
     
  5. Oct 20, 2014 #4
    Thanks.
     
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