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Homework Help: Hey can someone please help me

  1. Feb 12, 2010 #1
    I have two questions and i have no clue how to solve them so please...

    1. dropping a mass of M from some height H over a feid which is being covered with
    a lot of snow. exentually the mass is in halt underneath the snow in deep D
    the question is what is the average force that the snow is doing over the the mass during the process

    2. two parallel hoses are sitting on the ground. there is a third one which is equal to those two and is putting above them.
    the cofficient between the ground and the hoses is u1 and between hose 3 to the others
    is u2. the question is wether the hoses will move and how

    thank you very much. I am so lost...
    Kelly
     
  2. jcsd
  3. Feb 12, 2010 #2
    In the first problem, how much kinetic energy does the mass have when it reaches the snow? How much work, units of energy, must the snow do to stop the mass?
     
  4. Feb 14, 2010 #3
    hey thanks for answering me.
    I think i understand what you mean but therfore i would like to
    ask is what is actually stopping the mass?
    is it the friction (which i think that is countless here)
    or is it something else? i was thinking maybe it can be the getting into the snow..
    and still do i need calculate the time of all the process to get to the average force?
    i really apreciate your help!
    thank u very much
     
  5. Feb 14, 2010 #4
    Wait: have you learned work and energy yet? If not, you will have no idea about what I'm advising you to do.

    Yes, you can solve this problem using kinematics by assuming a constant acceleration of gravity until it reaches the snow and a constant acceleration from snow until it stops. Then, you can relate the acceleration of snow solved for to the force causing it through Newton's first law.

    Quicker, however, would be to say that all of the potential gravitational energy from being at a heigh H must be done by the snow by applying a constant force F over a distance D.

    About your question, you don't need to become too attached to understanding how the snow is applying the force doing all of this - just assume it's a constant force and solve for it. The force probably comes mostly from compressing the snow and partly from friction.
     
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