# Fluid dynamics: Knowledge continuity equation

Avalanche

## Homework Statement

Please click on the link for the question.

http://i1154.photobucket.com/albums/p526/cathy446/physicsquestion_zps49e16ab1.jpg

Assume that air spreads out after coming out from the tube at 2. The speed over tube 1 is almost zero.

## Homework Equations

Knowledge problem on fluid dynamics
Continuity equation A1v1 = A2v2

## The Attempt at a Solution

I know that the higher the liquid height of the tubes, the lower the air pressure. Higher flow speed also results in low pressure. So when the cross sectional area is large, the flow speed should be slow.

Using this reasoning, my answer was h2 > h4 > h3 > h1 but that answer is wrong.

Is something wrong with my logic?

Any help would be appreciated.

## Answers and Replies

Staff Emeritus
Homework Helper
I agree with your logic.

The fact that the author gave two options where h3>h4>h2, and leaves you to think about how the open-air height h1 relates to those in the tube, suggests that the author might have it backwards. Perhaps he or she was thinking about pressure, which has the reverse relation as the heights, i.e. p1>p3>p4>p2

Staff Emeritus