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Impulse Momentum for Linear

  1. Aug 8, 2012 #1
    1. The problem statement, all variables and given/known data
    Hi guys, just want to check is there any problem with the answer for part c and d of the question? I would really appreciate if you can help me double check, thank you.
     

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  3. Aug 8, 2012 #2

    NascentOxygen

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    Do you get their answers for (a) and (b)?
     
  4. Aug 8, 2012 #3
    yes but not for c and d
     
  5. Aug 9, 2012 #4

    NascentOxygen

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    I don't get anywhere near their answers for (a) or (b). :frown:

    I get their answers only if I change the force to 120 MN.
     
  6. Aug 9, 2012 #5

    ehild

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    For c) : Count gravity to the force that acts on the hammer+pile.

    ehild
     
  7. Aug 9, 2012 #6

    ehild

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    Have you used 8000 kg as mass of the hammer? (Mg = 103 kg)


    ehild
     
  8. Aug 9, 2012 #7

    NascentOxygen

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    Ah, with that correction all of my answers now are the same as those given alongside the question.
     
  9. Aug 9, 2012 #8
    Part C

    M1=mv
    =(9000)(8.82)
    =79380

    M2=mv
    =0

    I1-2=Force x Time
    =(F)(0.1)
    =0.1F

    M1+I1-2=M2

    79380-0.1F=0
    79380=0.1F
    F=793800 Ans Wrong


    Counting gravity force into working

    I1-2= Force x Time
    =(9.81F)(0.1)
    =0.981F

    79380=0.981F
    F=80917.43 Ans Wrong
     
    Last edited: Aug 9, 2012
  10. Aug 9, 2012 #9

    Doc Al

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    That's the net force acting. Use that to find the resistive force.
     
  11. Aug 9, 2012 #10
    Is I1-2= Force x Time this force always the net force?
     
  12. Aug 9, 2012 #11

    Doc Al

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    I'd say so.
     
  13. Aug 9, 2012 #12
    Can you guide me on how to use the net force to find the resistive force? Is there a formula to it?
     
  14. Aug 9, 2012 #13

    Doc Al

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    Draw a free body diagram and analyze the forces acting on the hammer+pile system.
     
  15. Aug 9, 2012 #14
    There is an action and reaction force. Action :+793800 Reaction-793800 :confused:
     
  16. Aug 9, 2012 #15

    Doc Al

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    For one thing, action and reaction forces act on different bodies. What you want are the forces acting on the hammer+pile.

    Second, that 793800 N force is a net force, not an individual force. So even talking about it as an "action" is meaningless.

    What forces act on the hammer+pile? Hint: Only two forces act.
     
  17. Aug 9, 2012 #16

    NascentOxygen

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    That's the opposing force to bring about the deceleration. In addition, you also have to oppose their weights, as well.
     
  18. Aug 9, 2012 #17
    Gravity and the 120kN external force?
     
  19. Aug 9, 2012 #18

    NascentOxygen

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    The specs indicate that the 120kN force is turned off by the time the soil opposes the moving pile.
     
  20. Aug 9, 2012 #19
    I just can't think of any other forces besides gravity.. and the FBD i drew looks abit weird to me too haha..:redface:
     
  21. Aug 9, 2012 #20

    NascentOxygen

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    How many newtons force UP must be exerted to balance their weights acting DOWNWARD?
     
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