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Homework Help: Final speed after dragging crate

  1. Oct 20, 2008 #1
    1. The problem statement, all variables and given/known data

    A 96 kg crate, starting from rest, is pulled across a floor with a constant horizontal force of 350 N. For the first 15m the floor is frictionless and for the next 15 m the coefficient of friction is .25. What is the final speed of the crate?

    2. Relevant equations

    Change in K = Work
    E + Ffr * d = 0
    1/2mv^2-1/2mv^2 + F(fr) d

    3. The attempt at a solution
    I broke this up into two steps. The first 15 m I took the Work done, set it equal to 1/2mv^2 and got the velocity for the beginning of the second reference frame . Somethings not working though because I get the incorrect answer. Am I setting this up incorrectly?
  2. jcsd
  3. Oct 20, 2008 #2
    Umm..I don't think you need to calculate anything for the Work. I don't see the need for the work. Find the acceleration using F=ma and put it into the correct kinematic equations to find the Vf of the first 15 m. Then take into account friction for the second have and use the same kinematic equation with the Vi being the Vf of the first 15 m.
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