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Homework Help: Potential Energy of a System

  1. Jan 1, 2012 #1
    1. The problem statement, all variables and given/known data

    a trophy being shown off by a careless athlete slips from the athlete's hands and drops on his toe.Choosing floor level as the y=0 point of your coordinate system,estimate the change in gravitational potential energy of the trophy-Earth system as the trophy falls.Repeat the calculation,using the top of the athlete's head as the origin of the coordinate.
    The trophy has a mass of 2 kg,and the top of a person's toe is about 0.03m above the floor.Also the trophy falls from a height of 0.5m.

    2. Relevant equations

    (? U)=(U final)-(U inetial)

    3. The attempt at a solution
    I'm not sure how to get started as I'm not good in solving equations of energ.
    I don't know how can I differentiate between potential energy & kinetic energy ??
     
  2. jcsd
  3. Jan 2, 2012 #2
    Do you know any eqn of potential energy of a body wrt earth ?
     
  4. Jan 2, 2012 #3
    Potential energy of gravity=mgy
     
  5. Jan 2, 2012 #4
    Yes. So What would be PE of system when trophy is in athlete's hands?
     
  6. Jan 2, 2012 #5
    PE=mg(y initial)=2*9.8*0.5=9.8J right??
     
  7. Jan 2, 2012 #6
    Yes.
    And similarly you can find the final PE ...
    Then change will be ____ ?
     
  8. Jan 2, 2012 #7
    OK thank you
    the change in PE will be approximately 9 J
    But is there any PE except gravitational PE???
     
  9. Jan 2, 2012 #8
    Yes. There are electric, magnetic etc
     
  10. Jan 2, 2012 #9
    OK thanks alot :)
     
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