# Homework Help: Multifluid manometer

1. Sep 8, 2010

### fishingspree2

1. The problem statement, all variables and given/known data
Hello
This is not a homework, but an example in my textbook that I don't really understand.

We need to find P1
The website I took this picture from explains it but it looks too complicated. The teacher did it moving along the tube and it looked really easy but I didn't understand. He almost did it in his head without using the board.

2. Relevant equations
pbottom = ptop +ρgh
the pressure at two points that have the same height are the same if they are connected with the same fluid.

3. The attempt at a solution
Find P1
Here's my try:

PE=Pairwatergh1
PE=PD
I don't know how to continue
I know I need to relate PD to the other known quantities but I don't really see how.

Another question: Isn't P1 = Pair ? Since 1 is at the boundary of air and water

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Last edited: Sep 8, 2010
2. Sep 8, 2010

### Staff: Mentor

No idea what P1 is.

I guess D means the point where the water and oil meet, B & C look well defined as well, but what are A & E?

3. Sep 8, 2010

### fishingspree2

P1 is the point where air and water meet.

the answer, if it helps, is:

P1 = Patm - ρwatergh1 - ρoilgh2 + ρmercurygh3

4. Sep 8, 2010

### Staff: Mentor

Go from the outside - if you know pressure at C (Patm), can you calculate pressure at B?