Homework Help: Fluid Manometer Question

1. Apr 29, 2013

LauraMorrison

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

The manometer illustrated in Fig. Q2 contains water and kerosene (specific
gravity of 0.82) as indicated. With both ends of the U-tube open the height
H0 =20 mm.
(i) Determine the height, h , when both ends of the tube are open. [4]
(ii) Determine the new value of H0 when a gauge pressure of 98 Pa is
applied to the right end of the U-tube. [6]

2. The attempt at a solution

I can do part (a), getting an answer of 91.1mm.

However, I am stuck on part (b).. I assume I cannot keep h constant and see the variation in Ho with the added pressure?

I am unsure how to work out the two unknowns h and Ho with only the one equation.

Attached Files:

• u-tube manometer.jpg
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2. Apr 29, 2013

Staff: Mentor

In part (i), you determined h, so, from the figure, you now know that total length of the kerosene column. This doesn't change in part (ii).

3. Apr 30, 2013

LauraMorrison

Are you sure h doesn't change? In my lecturers solutions it does change.. I don't really understand his solutions but maybe you can explain?

I have attached his solution.

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• manometersolution.docx
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4. Apr 30, 2013

Staff: Mentor

I didn't say h doesn't change. I said that the total length of the kerosene column doesn't change.

Chet

5. Apr 30, 2013

LauraMorrison

Oh I see, sorry I didn't read that carefully enough. Thank you I get it now! :)