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Work done on object vs work done by you

  1. Nov 9, 2014 #1
    What is the difference between work done on an object and work done by you?

    For example, you exert a 100N force pushing a 10kg mass 3.0m across the floor with a coefficient of friction 0.60
    1) what is the work done on the mass?
    2) what is the work done by you?

    For question 1 I think it has to do with a change in kinetic energy, and 2 with kinetic energy and heat energy, but I'm not sure how to solve? Thanks!
     
  2. jcsd
  3. Nov 9, 2014 #2
    Work done by you is manifest as sweat.
     
  4. Nov 9, 2014 #3
    But how do I solve these? What's the difference
     
  5. Nov 9, 2014 #4

    Simon Bridge

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    You should be able to see the difference by doing the calculation. Start from the equation for work.
    What is the total force on the mass? How far does it move?
    What is the total force on "you"? How far do "you" move?

    Basically: Things doing work lose energy.
    I think what they want you to notice is that not all the work done by "you" is done on the mass.
    Where else could your energy be going?
     
  6. Nov 9, 2014 #5

    ehild

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    The work done on the mass includes the work of all the forces, both yours and the force of friction (the work of the resultant force) which is equal to the change of kinetic energy.
    Recall: work is force times displacement. Your work is equal to your force times the displacement of the mass.
     
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