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Homework Help: Block Sliding, might use work energy theorum

  1. Jan 5, 2012 #1
    1. The problem statement, all variables and given/known data
    A block of mass 4.2 kg which has an initial velocity of 3.3 m/s at time t=0, slides on a horizontal surface.

    If a constant friction force of 10.2N is exerted on the block by the surface, what is the acceleration?

    2. Relevant equations

    Work Energy Theorum?
    .5 m vo2 - .5 m v22

    v = vo + at

    3. The attempt at a solution
    I found the kinetic energy of the block, then subtracted the 10.2N of friction. Then I solved for the second velocity. I plugged this into the acceleration equasion, but the answer was not correct? Can anyone help me?
  2. jcsd
  3. Jan 5, 2012 #2
    You might be over-thinking this one. What is Newton's Second Law?
  4. Jan 5, 2012 #3
    Using the work energy stuff is going to give you a second order differential equation with 2 boundary conditions to solve (initial and final velocity)
    Which is probably a bit harder than is required for this problem..

    There is however an equation which relates force to acceleration in a very simple way
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