True/False relating to Work

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  • #1
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Homework Statement


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


Homework Equations





The Attempt at a Solution


I thought they were all true except for the first one. But that isn't correct. Thanks!
 

Answers and Replies

  • #2
Doc Al
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That first statement is a bit ambiguous:
Work is done when the form of energy changes.
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?
 
  • #3
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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?

They're all true. Thank you for the help once again.
It's Physics for scientists and engineers
 
  • #4
Doc Al
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It's Physics for scientists and engineers
Who's the author? Fishbane, et. al.?
 
  • #5
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Who's the author? Fishbane, et. al.?

No, it is authored by Serway and Jewett.
 

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