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Moment or Work?

  1. Jan 7, 2013 #1
    Hey everybody,
    there's one little problem I've been working on for hours now, I'm usually not that bad however I couldn't imagine how to solve this using the given Information:

    1. Given Statement
    mK=3kg
    mL=2kg
    There's no friction
    -L is dropped without any speed, after falling 18 meters, what is the momentum(impuls? or sorry what ever it is lol..) affecting K in Newton.seconds

    Sorry for the bad English, thanks for the help

    One bad drawing of the problem


    2. Relevant equations
    1/2at^2=x
    mV=P
    F.Δt=m.ΔV


    The Answer is given as 9, though I couldn't formulate it into anything
     
  2. jcsd
  3. Jan 7, 2013 #2

    Doc Al

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    Staff: Mentor

    Why not try energy conservation?
     
  4. Jan 7, 2013 #3
    Is that possible without knowing the gravity of the system? If yes then how?
     
  5. Jan 7, 2013 #4

    Doc Al

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    Staff: Mentor

    What do you mean by "knowing the gravity" of the system? Isn't it on earth with normal gravity?
    Mechanical energy is conserved. (Look up mechanical energy and conservation of energy.)
     
  6. Jan 7, 2013 #5
    I'll try it again with conservation of energy, but no it's not necessarily on Earth.
     
  7. Jan 7, 2013 #6

    Doc Al

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    Staff: Mentor

    If it's not on earth, I don't see how you can solve the problem. Not enough information.

    Can you state the problem word for word as it was given? (What makes you think it's not on earth?)
     
  8. Jan 7, 2013 #7
    In a system in which friction is unimportant, the bodies K and L are released. When body L has dropped 18 meters, what is the Impuls given K in kg.m/(s^2).s=N.s

    I assume it's not on earth because if it was the result couldn't be 9, and the book the question is from usually states the gravity either as 9.8 or (in some questions) 10.
     
    Last edited: Jan 7, 2013
  9. Jan 7, 2013 #8

    Doc Al

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    Staff: Mentor

    OK, clear enough.

    I agree that the answer cannot be 9, but I suspect that's just an error in your problem statement or answer key. Unless they tell you otherwise, I would assume the set up is on Earth!

    Show how you would solve the problem and then we can see if you're on the right track or not, regardless of the given answer.
     
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