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Force necessary to support mass on Hydraulic Jack?

  1. Aug 17, 2009 #1
    Force necessary to support mass on Hydraulic Jack???

    1. The problem statement, all variables and given/known data
    Piston 1 in the figure has a diameter of 1.31 cm. distance of 2 in
    Piston 2 has a diameter of 7.91 cm. distance of 10 in
    In the absence of friction, determine the force F, necessary to support an object with a mass of 904 kg placed on piston 2. (Neglect the height difference between the bottom of the two pistons, and assume that the pistons are massless).

    2. Relevant equations
    F1*d1 = Fp*d2, where d1 is the moment arm of F1, and d2 is
    the moment arm of Fp.

    3. The attempt at a solution
    Fp = (F1*d1)/d2
    (904)(9.81)/(pi)(0.003955)^2= F/(pi)(0.00655)^2
    F=242.98 N which was incorrect.
    anyone have an idea of what I should do and what equation to use? Thanks!
     
  2. jcsd
  3. Aug 17, 2009 #2

    Redbelly98

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    Re: Force necessary to support mass on Hydraulic Jack???

    I think we'll need to see the figure before we can help you out.
     
  4. Aug 17, 2009 #3
  5. Aug 17, 2009 #4

    djeitnstine

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    Re: Force necessary to support mass on Hydraulic Jack???

    Neglecting the height difference means the pressure should be the same, thus [tex]F_1 A_1 = F_2 A_2 [/tex]

    This is would be the force exerted on the small piston.

    You should know how to find the force needed by the hand from this.
     
  6. Aug 17, 2009 #5

    Redbelly98

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    Re: Force necessary to support mass on Hydraulic Jack???

    You have correctly found F1, the force on the smaller piston. However, they are asking for Fp (labelled simply F in the figure), the force exerted by the hand.

    You have the equation to find Fp given F1.
     
  7. Aug 18, 2009 #6
    Re: Force necessary to support mass on Hydraulic Jack???

    ok. I used the equation given and solved for Fp. I had (242.98)(pi*(0.03955)^2))/(pi)*(0.00655)^2=Fp=8858.92 N, which is also incorrect.
    what am I doing wrong?
     
  8. Aug 18, 2009 #7
    Re: Force necessary to support mass on Hydraulic Jack???

    nvm. I solved it! thanks everyone for your input!
     
  9. Mar 1, 2011 #8
    Re: Force necessary to support mass on Hydraulic Jack???

    how u solved it my friend?
     
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