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Force/Work Problem (help needed)

  1. Dec 17, 2005 #1
    A 100.0 kg block moves across a surface where the coefficient of friction9kinetic) is 0.10. The block is pushed horizontally with a force equal to 40% of its weight. How much work does the pushing force do in moving the block 100.0m? How much work does friction do? What is the change in velocity? How much greater would the change in velocity be if there was no frictional dissipation of energy involved?


    For this probelm I get 39200J for the work done by the pushing force and I get 9800J for the work done by friction. Are these answers correct? THen I have no idea how I would find the change in velocity? Any suggestions?
     
  2. jcsd
  3. Dec 17, 2005 #2

    Dale

    Staff: Mentor

    You are correct about your numbers for the work done by pushing and by friction.

    The pushing force does work on the object, so we are adding energy to the object. Since we are pushing it horizonatlly, the energy can either go to KE (velocity of the object) or heat (from the friction). So just take the work done, subtract the energy that goes to heat, that is the change in KE. Then convert from a change in KE to a change in velocity. This approach makes the second part (with no friction) very easy since you just have no energy going to heat.

    -Dale
     
    Last edited: Dec 17, 2005
  4. Dec 17, 2005 #3
    Great thanks I got it now!
     
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