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Homework Help: Work? maybe just kinematic (please help! I don't even know what it is!)

  1. Oct 16, 2006 #1
    Work?....maybe just kinematic...(please help! I don't even know what it is!)

    The spring shown in the figure is compressed 50 cm and used to launch a 100 kg physics student. The track is frictionless until it starts up the incline. The student's coefficient of kinetic friction on the 30 degree incline is 0.15.

    http://session.masteringphysics.com/problemAsset/1000852/6/knight_Figure_11_54.jpg

    What is the student's speed just after losing contact with the spring?

    How far up the incline does the student go?

    The v_initial is incredibly easy to find, 14.1, but I can't seem to find how far he travels up the incline.
    I've set it up a few different ways, and each time I get the wrong answer.

    if Fx = -F_f - F_w*sinθ = ma
    Fy = n - F_w*cosθ = 0 -> n = m*g*cosθ

    then shouldn't -umgcosθ - mgsinθ = ma
    giving you a = -g(ucosθ + sinθ) ?

    and then the distance could be solved using the v_initial and a using kinematics?
    But it is wrong? Could someone please explain?
     
  2. jcsd
  3. Oct 16, 2006 #2
    never mind found it
     
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