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RE:hydraulic pump

  1. Jun 16, 2005 #1
    these are following information given:
    2 cylinders with diameters of 50mm and 150mm are connected.
    specific gravity of oil=0.8
    then on top of the cylinder with the larger diameter is a 500kg mass.
    so the question is on what is the force required on the smaller diameter?
    another information from the diagramm is that the height of oil is the same at both cylinders but the value is not given.

    1st)since height of fluid is same i know p1=p2

    2nd)i find force exerted by the 500kg mass:f=mg

    3rd)i know force =pressure x area:so by rearranging i can find pressure.

    i have a doubt over here:is area=pi x r^2 / or is area=surface area of cylinder(but i do not know height therefore i assume its t 1st 1)

    4)since i now know how to find pressure:p1=p2, therefore i have just gotta use the formula i used in step 3 again to find force @ smaller diameter

    what worries me here what is purpose of the question giving the specific gravity of oil?i know i can find density of oil from there but to me its doesnt help me in solving the qns.i am worried i am going somewhere wrong in the question.thanks in advance for those who take their time off to help me in this question.
    Last edited: Jun 16, 2005
  2. jcsd
  3. Jun 16, 2005 #2


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    If the surface of the cylinder is a circle, they are the same. Are you given other information?

    I don't see that the specific gravity of the oil has anything to do with these questions.
  4. Jun 16, 2005 #3


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    1: Correct
    2: Is it 200 kg or 500 kg? F=mg is the correct way to go.
    3: Correct again.
    4: The area is the cross sectional area of the piston (circle).

    There really is no need for the specific gravity. The only assumption you make is that the fluid is incompressible. The only other thing I would mention is that the actual question is phrased poorly and is a bit incomplete in terms of what you are looking for. "...what is the force required on the smaller diameter?" Force required to do what? Do the cylinders move at all or is the force required to maintain the current level of the cylinders?

    EDIT: HallsofIvy beat me to it...
    Last edited: Jun 16, 2005
  5. Jun 16, 2005 #4
    thanks to both u guys for clearing my doubts.basically the force at the smaller diameter is just to maintain the current level.sorry for not having that mentioned earlier.and also sorry for the part i made a typo on the mass.haha just got too excited i suppose.
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