# Homework Help: Pressure in U-tube

1. Aug 25, 2009

### songoku

1. The problem statement, all variables and given/known data
Two liquids A and B of densities 1.0 g cm-3 and 0.8 g cm-3 are poured into an U-tube as shown in the figure below. Find x !

2. Relevant equations
$$P = \rho g h$$

3. The attempt at a solution
Is it possible liquid A is on top of liquid B because A has higher density than B?

Or do I misinterpret the question? Is it possible the question means density of A is 0.8 g cm-3 and B is 1.0 g cm-3 because there is no word "respectively" ?

Thanks

2. Aug 25, 2009

### Staff: Mentor

Sure, why not? Look at the diagram. Note that the height of liquid A is less than that of liquid B. There's a reason for that!

3. Aug 25, 2009

### kuruman

The statement looks correct, A is more dense than B. At the line PQ the pressure is the same. So more height of liquid above point P is needed to maintain the pressure the same as at point A.

4. Aug 25, 2009

### songoku

Hi Doc Al and kuruman

Oh so it's possible that liquid with higher density is on top of liquid with lower density. I always think it's impossible.

I get it now. Thanks a lot Doc Al and kuruman ^^

5. Aug 25, 2009

### ideasrule

Just imagine an iron piston pressing down on water in the U-tube and you'll see why it's possible.