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Homework Help: Work done on the block by force

  1. Jul 23, 2009 #1
    1. The problem statement, all variables and given/known data

    A block is pushed across a rough horizontal surface from point A to point B by a force (magnitude P = 5.4 N) as shown in the figure. The magnitude of the force of friction acting on the block between A and B is 1.2 N and points A and B are 0.5 m apart. If the kinetic energies of the block at A and B are 4.0 J and 5.6 J, respectively, how much work is done on the block by the force P
    between A and B?

    2. Relevant equations
    W= PCos (theta)D

    3. The attempt at a solution
    I have no idea what to do for this!
  2. jcsd
  3. Jul 23, 2009 #2
    I suppose Work done on the block = change in kinetic energy + work against friction
  4. Jul 23, 2009 #3


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    Science Advisor
    Homework Helper

    Welcome to PF!

    Hi Zmuffinz! Welcome to PF! :smile:

    (have a theta: θ :wink:)
    Well, what is θ in this case? :smile:
  5. Jul 25, 2009 #4
    well you see thats why im stuck, i wasnt given an angle, or mass of the block or anything so ive got no clue as to what to do:(
  6. Jul 25, 2009 #5
    and how do i calculate work against friction?
  7. Jul 25, 2009 #6

    Doc Al

    User Avatar

    Staff: Mentor

    You didn't post the diagram, but I presume that the force was applied horizontally. That will tell you all you need about angles.
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