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True/False relating to Work

  1. Oct 20, 2010 #1
    1. The problem statement, all variables and given/known data
    Work is done when the form of energy changes.
    Work cannot be done in the absence of motion.
    Energy conservation law for a projectile (no friction): Potential energy increase equals the kinetic energy decrease.
    Without friction, and in the absence of external forces, the sum of the potential and kinetic energies of a body is constant.
    Energy is required to do work.
    Less power is required while slowly lifting a box than while lifting it up quickly.
    Problem Weight is: 1


    2. Relevant equations



    3. The attempt at a solution
    I thought they were all true except for the first one. But that isn't correct. Thanks!
     
  2. jcsd
  3. Oct 21, 2010 #2

    Doc Al

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    Staff: Mentor

    That first statement is a bit ambiguous:
    Strictly speaking, this is equivalent to "If the form of energy changes, then work was done." Which is not true as a general statement, but depending on the context of your course may be considered true in some limited sense.

    The other statements are less ambiguous and are true, so I suspect your book wants you to treat this as true as well.

    What book are you using?
     
  4. Oct 21, 2010 #3
    They're all true. Thank you for the help once again.
    It's Physics for scientists and engineers
     
  5. Oct 21, 2010 #4

    Doc Al

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    Staff: Mentor

    Who's the author? Fishbane, et. al.?
     
  6. Oct 21, 2010 #5
    No, it is authored by Serway and Jewett.
     
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