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Homework Help: Block, Ramp, Friction, and Spring Due Tomorrow

  1. Oct 6, 2008 #1
    Block, Ramp, Friction, and Spring Due Tomorrow!!

    1. The problem statement, all variables and given/known data

    A man pulls a block of mass m = 17 kg up an incline at a slow constant velocity for a distance of d = 3.5 m. The incline makes an angle q = 33° with the horizontal. The coefficient of kinetic friction between the block and the inclined plane is µk = 0.4.
    a) What is the work Wm done by the man?

    Wm = 513.45J OK

    HELP: Draw a free-body diagram of the block.
    At the top of the incline, the string breaks and the block, assumed to be at rest when the string breaks, slides down a distance d = 3.5 m before it reaches a frictionless horizontal surface. A spring is mounted horizontally on the frictionless surface with one end attached to a wall. The block hits the spring, compresses it a distance L = 0.6 m, then rebounds back from the spring, retraces its path along the horizontal surface, and climbs up the incline.

    b) What is the speed v of the block when it first reaches the horizontal surface?

    v = m/s

    HELP: Use the work-energy theorem.
    HELP: What is the work done on the block by gravity? What is the work done on the block by friction? The sum of these two numbers will equal the kinetic energy of the block at the bottom of the incline.

    c) What is the spring constant k of the spring?

    k = N/m

    d) How far up the incline d1 does the block rebound?

    d1 = m

    So I am stuck on part b)
    Here's what I did:
    2. Relevant equations
    KE=PE - Wf= mgh - mumgcosq.
    so, v=sqrt(2KE/m)=sqrt(2(gh-mugcosq)

    3. The attempt at a solution
    To calculate h I tried sinq=h/d so h=dsinq= 3.3

    I plugged this in and got v=sqrt(2(9.81*3.3-.4*9.81*cos33))= 5.5m/s
    I also tried to add PE and Wf. What am I doing wrong?
  2. jcsd
  3. Oct 7, 2008 #2
    Re: Block, Ramp, Friction, and Spring Due Tomorrow!!

    I got a similar question. For part b I tried v = sqrt 2(gh- ug cos 33). It should work however I'm having trouble w/ it.
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