tim asked in Science & MathematicsPhysics · 5 years ago

Physics Manometer Question?

I've established P1 at the lower end of the 69.9cm mark. (0.669m) and calculated

P1= Pgas + roh*g*h

= 93,643.5 Pa

Established P2 directly horizontal at the point where the Water and Oil meet,


P2=Patm + ro*g*h

solving for h, i get -0.7498...m,

What am i doing wrong here?

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1 Answer

  • NCS
    Lv 7
    5 years ago
    Favorite Answer

    On the LHS, P1 = Patm + rho*g*H.

    where rho is the density of water.

    From the same base mark on the RHS, you have

    P1 = Pgas + RHO*g*0.699m

    where RHO is the density of the oil.


    Patm + rho*g*H = Pgas + roh*g*h

    1.01e5Pa + 1000kg/m³ * 9.8m/s² * H = 0.88e5Pa + 823kg/m³ * 9.8m/s² * 0.699m

    H = -0.751 m

    I, too, get a negative number, and very close to yours.

    Either the gas pressure is too low, or the head of oil is too small, or the oil's density is too low.

    I believe that the gas pressure SHOULD have been 98 kPa, not 88 kPa. Then

    1.01e5Pa + 1000kg/m³ * 9.8m/s² * H = 0.98e5Pa + 823kg/m³ * 9.8m/s² * 0.699m

    H = 0.269 m

    Et voila!

    If you find this helpful, please select Best Answer!

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