TBR Physics Example 7.2a

[pnoybballin]

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Could someone please help me in clarifying Example 7.2a of TBR Physics Book 2? I understand the first part;

2Patm = Patm + pgh -> pghinitial = Patm

But how did they get pghfinal = 3Patm for the second part? Thanks a lot everyone!

 

[pnoybballin]

Eh, could someone also go about explaining the problem after that Example 7.2b. Thanks so much everyone.

 

[geh926]

bump? 🙄

 

[Pisiform]

Well,

P_total = P_atms + (rho)gh

For first scenario: 2 P_atms = P_atms + (rho)gh

Make (rho)gh the subject: (rho)gh = 2P_atms - P_atms = P_atms

For second scenario: P_total = P_atms + 2(rho)gh

plug in: P total = Patms + 2(P_atm)

P total = Patms + 2Patms = 3 P_atms

so total Pressure changed from 2 P_atms ---> to 3 P_atms, so pressure change in percentage is: change in pressure/original * 100 = 1 / 2 * 100 = 50%

 

[Warren Peace]

For 7.2a:

The total pressure = pressure due to atmosphere + pressure due to liquid in the pool. They say initially, a barometer measures the total pressure to be twice that of atmospheric pressure. So total pressure = 2 atm (with 1 atm due to atmosphere and 1 atm due to liquid pressure) at the initial depth.

Then they submerge the barometer twice as deep. This serves to double the pressure due to the liquid (now 2atm instead of the initial 1). Thus, total pressure = 1 atm (atmosphere) + 2 atm (liquid) = 3 atm

3 atm is 50% more than 2 atm, so the pressure increases by 50%

For 7.2b, I think the book explains it well

EDIT Son of a gun! Pisiform beat me to it!

 

[SN2ed]

Thread moved. These types of threads belong in the Study Q&A forum.

 

[Aromatic Amine]

For 7.2a:

The total pressure = pressure due to atmosphere + pressure due to liquid in the pool. They say initially, a barometer measures the total pressure to be twice that of atmospheric pressure. So total pressure = 2 atm (with 1 atm due to atmosphere and 1 atm due to liquid pressure) at the initial depth.

Then they submerge the barometer twice as deep. This serves to double the pressure due to the liquid (now 2atm instead of the initial 1). Thus, total pressure = 1 atm (atmosphere) + 2 atm (liquid) = 3 atm

3 atm is 50% more than 2 atm, so the pressure increases by 50%

For 7.2b, I think the book explains it well

EDIT Son of a gun! Pisiform beat me to it!

this is a spot on answer. thanks a bunch. really made me understand it. side career as a teacher?! 😀