# Pressure in a gas container measured with a barometer and a U pipe

• Callmelucky
In summary, the conversation discusses the calculation of gas pressure in a container with a U-shaped pipe attached, using the height of the pillar of mercury in a barometer. The person provides their solution, which results in a pressure of 105398.64 Pa, while the textbook's answer is 100062 Pa. The person questions the accuracy of the textbook and asks for confirmation of their solution. It is also noted that the barometer is not shown in the picture. The conversation concludes with an explanation that the U tube links the outside world with the inside of the container and the effect of changing ambient pressure on the 5 cm measurement.
Callmelucky
Homework Statement
to a container filled with gas, U shaped pipe is attached, as shown in the picture(picture below). What is a gas pressure in the container if the height of the pillar of mercury in barometer is 740 mm?
Relevant Equations
pressure = density * g * height
Can someone please tell me where I am wrong, here goes the question:

to a container filled with gas, U shaped pipe is attached, as shown in the picture(picture below). What is a gas pressure in the container if the height of the pillar of mercury in barometer is 740 mm?

The way I solved it is: pressure of mercury(740mm) + 5 cm difference in U pipe --> 0.740 m * 13600 * 9.81 + 0.05 * 13600 * 9.81 = 105398.64 Pa. But the answer at the and of the textbook is 100 062 Pa.

Thank you.

#### Attachments

• IMG_20230205_010729_edit_967933005698658.jpg
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Any chance the textbook is wrong ?

I find somewhat different conversion factors, but with three digit accuracy the 105 kPa stands firmly.
mm Hg to Pa
density of Hg

(you can't find a seven digit result from a three digit factor)

Callmelucky
it seems that this textbook is full of flaws.
Can you check my previous post(from an hour ago or so), I think my answer is correct and their wrong on that one too.

Where is the 740 mm height of mercury? Oh, never mind. It's in a barometer that is not shown.

Callmelucky
erobz said:
Where is the 740 mm height of mercury? Oh, never mind. It's in a barometer that is not shown.
That is another thing, if it's gas, I guess that container couldn't be filled on normal pressure(atm), so I don't understand what does pressure outside container(thoose 740 mm Hg) has to do with pressure inside of gas?

The U tube links the outside world with the inside of the container. Ask yourself what happens to the 5 cm if the ambient pressure changes.

Callmelucky and erobz
BvU said:
The U tube links the outside world with the inside of the container. Ask yourself what happens to the 5 cm if the ambient pressure changes.
thanks, that makes sense.

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