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Homework Help: Calculate the work done by friction of package

  1. Oct 10, 2008 #1
    1. The problem statement, all variables and given/known data

    A 5.00 kg package slides 1.50 m down a ramp that is inclined at 12 degrees below horizontal. The coefficient of kinetic friction is 0.310.
    a- Calculate the work done by friction.
    b- Calculate the work done by gravity.
    c- Determine the net work done on package.
    d- If thepackage started sliding with a speed of 2.2 m/s, find the final speed.

    2. Relevant equations

    Fk = n * coefficient
    W = Fd cos angle
    K= i/2 mv^2

    3. The attempt at a solution

    a-
    n (Normal) = wcos 12= 47.9 N
    Fk (Friction) = normal * coefficient = 14.8N
    Work Fk = 1.5m * 14.8 N * cos 180 = -22.2 J

    b-
    wsin12 * 1.5m * cos 0 = 15.3 J

    c-
    W total = 15.3J - 22.2 J = -6.9 J

    d-
    1/2 m v init ^2 - 6.9 J = 1/2 m vfinal ^2

    12.1 J - 6.9 J = 2.5 kg v final ^2

    v final = 1.44 m/s


    I was feeling pretty good about this, but I showed it to someone in my school's math lab and he told me he thought it was all wrong. He said I need to break every force in x and y components. I don't see why I would. I would appreciate it if someone could tell me if I am doing this correctly.
     
  2. jcsd
  3. Oct 10, 2008 #2

    Doc Al

    User Avatar

    Staff: Mentor

    You are correct.
     
  4. Oct 10, 2008 #3
    Alright! Thank you.
     
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