# Absolute pressure

## Homework Statement

the question is in the diagram i have attached. basically i have to find absolute pressure

## Homework Equations

P = pgh where P is Pressure and p is density

## The Attempt at a Solution

1st of all i need to convert 750mm into a pressure? somehow dont know exactly.

the rule i was told is starting from the right side, if it goes down it is subtracted and if it goes up it is added. So in knowing that i did: p_atm - (8 * 0.15 ) - ( 10* 0.05) but i dont know the pressure yet coz i dont know how to calculate. is the rest of the method correct though?

#### Attachments

• aaaaaa.png
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tiny-tim
Homework Helper
Hi TyErd!
1st of all i need to convert 750mm into a pressure? somehow dont know exactly.

(you mean 758 )

758 mm of Hg means the pressure at the bottom of a tube of Hg 758mm high …

so you need to know the density of Hg.
the rule i was told is starting from the right side, if it goes down it is subtracted and if it goes up it is added. So in knowing that i did: p_atm - (8 * 0.15 ) - ( 10* 0.05) but i dont know the pressure yet coz i dont know how to calculate. is the rest of the method correct though?

Isn't it adding for both of them?

You start with atmospheric https://www.physicsforums.com/library.php?do=view_item&itemid=80" and then it increases when you go down …

don't you have to go down from the interface to that little arrow?

Last edited by a moderator:
okay i get how to calculate the atmospheric pressure now. According to my book and a couple of questions completed with a teacher, If you are starting from the left, you add as you down and subtract as it goes up. And I think he said if you start from the right side, its add if you up and subtract if you go down. I'm not too sure, I need someone to confirm it thats right or not.

tiny-tim