TBR Fluids and Solids- 7.2b

[bonitanolita]

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

C. tot pressure decreases by 33%
D. total pressure decreases by 66%

I've narrowed the answer choices down to C and D because I know total pressure will decrease as you reach the surface. However I dont know how to det Patm at the bottom and at the surface. The correct answer is D. Any help appreciated!

 

[shffl]

Hmm I'm interested in this one as well. Does anyone care to explain because I got C. Here's what I did:

P = Patm + pgh (assuming P at surface = Patm)

Since pressure at surface is 1atm, then

P = 1.5atm
Patm = 1atm
pgh = 0.5Patm

Therefore at 5m depth P = 1.5atm. When the swimmer goes back to the surface, P = 1atm. A change of 1.5atm to 1atm is a decrease of 33%

 

[BerkReviewTeach]

Bonitanolita: do you have the older version that doesn't list explanations for the B questions? I don't have that version still, so I can't verify what letter is listed in the key. But from my current book and my solution, I agree with shffl that C is the correct answer.

As was stated, Ptotal = Patm + pgh

The total pressure at surface is 1atm, so at a depth of 5m, the total pressure is 1.5 atm.

Ptotal = 1.0 atm + 0.5 atm

The swimmer goes from Ptotal = 1.5 atm to Ptotal = 1atm, so the total pressure has decreased by 33%.

 

[bonitanolita]

Thanks for the explanation! and yeah I guess I have the older book now, but I ordered it this past September? Is the updated version that much different?

 

[bonitanolita]

And yes C is the right answer. I read the wrong answer choice