Physics: Fluids & Solids

[pnoybballin]

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Could someone please help me out on how to go about solving these 2 questions? Thanks a lot!

1) At a specific depth in a swimming pool, a barometer measures the total pressure to be twice that of the atmospheric pressure. If the barometer is now submerged to a depth that is twice its initial depth, by how much does the total pressure increase?

A. The pressure increases by 50%
B. The pressure increases by 100%
C. The pressure increases by 200%
D. The pressure increases by 300%

The answer is A.

2) A swimmer is at the bottom of a 5-meter pool, where the gauge pressure (pgh) is approximately 0.5Patm. If the swimmer rises to the surface, by how much does the total pressure change?

A. The total pressure increases by 33%
B. The total pressure increases by 66%
C. The total pressure decreases by 33%
D. The total pressure decreases by 66%

The asnwer is C.

 

[dragon529]

These are from TBR... with explanations...
Anyways..

1.P (total) = P (atm) + P (gauge)
Since at a certain death... it measures to 2 atm, that means P (atm) = 1 and P (gauge) = 1 to make P (total) = 2. Now, since the depth has increased 2x, we expect P (gauge) to expect 2x as well. So the new P (total) = 1 + 2 = 3. Since the change was from 2atm ---> 3 atm, the pressure increased by 50%.

2.
At the bottom of the pool...P (total) = 1 + 0.5 = 1.5
When he rises to surface... P (total) = 1 + 0 = 1
The difference of pressure is (1.5-1) / 1.5 = 0.33... and pressure decreases because pressure is lower up top then at the bottom..

Hope that helps..

 

[ThirdEye]

1.
The pressure felt is provided by both water and gas, thus the pressure of the water alone is 1 atm since the total pressure is 2 atm. So if you increase the depth, you're now experiencing 2 atm from water and 1 atm from gas. A change in total pressure from 2 to 3 is an increase in 50%.

2.
For the second question, the gauge isn't including the atmosphere. The total pressure is 1.5 atm. So the change in pressure is from 1.5 atm to 1 atm, which is a decrease of 1/3.

 

[Oh_Gee]

1.
The pressure felt is provided by both water and gas, thus the pressure of the water alone is 1 atm since the total pressure is 2 atm. So if you increase the depth, you're now experiencing 2 atm from water and 1 atm from gas. A change in total pressure from 2 to 3 is an increase in 50%.

2.
For the second question, the gauge isn't including the atmosphere. The total pressure is 1.5 atm. So the change in pressure is from 1.5 atm to 1 atm, which is a decrease of 1/3.

ah still confused. so let's say the initial depth was 2 meters below the surface and the initial reading was 2Patm. then the barometer goes twice the distance (4 meters). wouldn't the final pressure be 4Patm?

ah nvm i just drew it out and figured it out. really sorry for bumping this

 

[el_duderino]

How do you get 4 atm? Every 2 meters would be 1 atm (which it isn't; it's more like 0.2 atm, but that doesn't matter). You don't increase 1 atm in the first 2 meters and 2 atm in the second 2 meters. It's 1 atm per 2 meters.

 

[Oh_Gee]

How do you get 4 atm? Every 2 meters would be 1 atm (which it isn't; it's more like 0.2 atm, but that doesn't matter). You don't increase 1 atm in the first 2 meters and 2 atm in the second 2 meters. It's 1 atm per 2 meters.

yeah sorry i just drew a picture after i posted and figured it out lol