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Pressure Problem

  1. Mar 1, 2007 #1
    Pressure: how much force is needed on the small piston to lift the car?

    1. The problem statement, all variables and given/known data

    A hydrolic piston with a radius of 1 inch is connected with a hose to a piston with a radius of 5 inches. There is 1000 kg (9800N) car sitting on top of the large piston. How much force is needed on the small piston to lift the car?

    2. Relevant equations

    14.7 psi = lb/in^2
    circumference = 2 x 3.14 x radius
    Area of a circle = 3.14 x radius^2
    lbs / in^2
    P = F / A
    F = PA

    I'm guessing... these are somewhat my formulas.

    3. The attempt at a solution

    So far, this is what I attempted, but I'm pretty sure it's not correct because it is very rare I am right.

    1000 kg/ (3.14 x 5^2 in^2) = 7957.7 psi

    7957.7 psi x 3.14 = 24999.9 lbs

    Plus, I think I should use 9800N at least sometime in this problem. Please tell me what I should change and what steps I should take. And then help me figure the Ideal Mechanical Advantage (I. M. A.) of the hydraulic system?
    Last edited: Mar 1, 2007
  2. jcsd
  3. Mar 2, 2007 #2
    you want to know the force on the small piston that will cause a pressure large enough for the bigger piston to overcome the weight of the car

    be careful with your units, a kg/in^2 is not a pressure (you want a N/m^2 or a lb/in^2)

    you have the force for the big piston, (the force that you want the big piston to overcome), you have the area for the big piston...so what else can you find out?

    P = F/A

    and what do you know about the pressure on the big piston and the small piston?
  4. Mar 2, 2007 #3
    Remember, pressure in = pressure out! This is the unifying link between both positions and you will find yourself able to solve this problem much more easily.
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