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Homework Help: Energy conservation

  1. Dec 8, 2007 #1
    Hello,
    I have one problem...

    In what initial speed must barmen throw beer mug on the table so it can travel 2 meters. Mass of the beer mug is 0,3 kg. Sliding loss factor between table and beer mug is 0,3.

    I hope you have understand the question, because I am translating it from my mother language and some of terms are new to me...

    I have to solve this problem using energy conservation principle.

    So kinetic energy is wasted on (abrasion, attrition, friction, rub, Sliding loss - which is the right term):
    Ek=W
    W is F*s
    F is m*g*u

    It now becomes:

    1/2*m*v^2=m*g*u

    This can't be right... Mass is relevant here but with this equation it is equation abridged...
     
  2. jcsd
  3. Dec 8, 2007 #2

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    I'm not quite sure what exactly you mean by "sliding loss factor". If it is just the co-efficient of kinetic friction, then the result is independent of m. The initial speed would be 3.43 m/s.

    If that is the case, then ma = -0.3*mg and v^2 = -2ax, giving the value of v.

    If it means something else, please let us know.
     
  4. Dec 8, 2007 #3
    I looked up for the right term, yes I thought on Coefficient of friction which is 0,3.

    But i need solve this with energy conversation...
     
  5. Dec 8, 2007 #4

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    Equate work done by frictional force to initial KE.
     
  6. Dec 8, 2007 #5
    When you solve this

    Kinetic energy = frictional force * x
    Ek=F*x

    You get 1,71 m/s

    So which is correct?

    1,71 or 3,43 m/s?
     
  7. Dec 8, 2007 #6

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    Show your calculation.
     
  8. Dec 8, 2007 #7
    No, I made a mistake, it is 3,43.


    Thank you.
     
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