Fluid Manometer Question: Determining Height and Pressure

[LauraMorrison]

Homework Statement

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 H_o with the added pressure?

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

 

[Chestermiller]

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).

 

[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.

 

[Chestermiller]

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.

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

Chet

 

[LauraMorrison]

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