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Homework Help: Friction and final velocity

  1. Nov 6, 2007 #1
    1. The problem statement, all variables and given/known data

    A block starts from rest at a height of 4:6 m on a fixed inclined plane.
    The acceleration of gravity is 9.8 ms^2. The box is 3.9 kg. The coeffiecient of friction is 0.18. The angle of the ramp from the ground up is 35 degrees.
    What is the speed of the block at the bottom of the ramp? Answer in units of m=s.

    If the block continues to slide on the ground with the same coeffcient of friction, how far
    will the block slide on the ground until coming to rest? Answer in units of m.

    SO lost...
  2. jcsd
  3. Nov 6, 2007 #2
    You should begin by identifying all the forces acting on the block, and use Newton's Second Law to find the net force on the block. Once you know the net force, you know the acceleration of the block, which should be constant, and since it is we can use the kinematic equations to find its velocity at the bottom of the ramp.
  4. Nov 6, 2007 #3
    first you have to find Fgx, which is mgsin(35). but your total is Fgx-Fk.

    to find Fk, you need to find Fn, which is mgcos(35). from your coeffiecient of friction, you can find Fk, MkFn=Fk which is (.18)(mgcos(35))

    when you find Fgx-Fk, you set that equal to ma, find acceleration and then use position function to find your velocity. vt+1/2at^2=x
  5. Nov 6, 2007 #4
    Looks good to me, let me know if you get hung up.
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