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Homework Help: Block pulled on horizontal surface -w/friction-

  1. Oct 2, 2011 #1
    1. The problem statement, all variables and given/known data
    A box weighing 80N is pulled along a horizontal surface by a force of 15 N which is directed at 20° above the horizontal. If the box started from rest and the coefficient of friction is 0.15, find the kinetic energy and velocity of the box after it traveled a distance of 10 m.

    2. Relevant equations
    Normal force= W-Tsinθ
    Frictional force=μk x Normal force

    3. The attempt at a solution
    First I looked for normal force which turns out as 74.87 then frictional force which is 11.23 after that, I dont get how to find velocity. I just need final velocity at this point to get average velocity=velocity then having V, I could solve for K.E.
    Last edited: Oct 2, 2011
  2. jcsd
  3. Oct 2, 2011 #2
    Force accelerates the box's speed.
    It has a speed of 0m/s in the beginning.
    [itex]x = x_0 + v_0t + 0.5at^2[/itex]
    [itex]x = 0.5at^2[/itex]
    On the other hand
    [itex]v_{end} = v_0 + at[/itex]
    [itex]v_{end} = at[/itex]
    Should be all the info you need. Think about it.
  4. Oct 2, 2011 #3
    would just like to clear the following things:
    -what does x,x0,v0 stand for? (guessing that 0 there means zero)
    -does a stand for acceleration while t is time?
  5. Oct 2, 2011 #4
    They're the basic equations of motion.
    x = total distance
    x_0 = distance from origin(usually 0 unless origin is set somewhere else than on the system you're investigating)
    v_0 = speed the system has when you begin investigating it
    a = acceleration
    t = time
  6. Oct 2, 2011 #5


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    Staff: Mentor

    If you know the net force F moves the block, acting in the direction of motion, then the work done on the block moving it distance d is given by F*d. Where does that work end up (how is it expressed in the system)?
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