Every time I come across this kind of question, I would find myself spending a lot of time on it or get it wrong, Can you please let me know the GENERAL approach and basic logics I should use when it comes to this type of problem? I know this problem is very basic but how
“If a patient’s original lung volume (V1) is decreased by 33% (V2), what’s the relationship between the total pressure in the patient’s lungs before (p1) and after (p2) this change?
The correct answer: P2= 3/2 P1
How I approached this on the test, and this took forever:
V1  33% = V2= 1  33% = 67%
And then I’m stuck there
Thank you!
Basic question: need help

 Posts: 48
 Joined: Wed May 27, 2020 7:25 pm
Re: Basic question: need help
Hey!
For this one, remember Boyle's Law which tells us the pressurevolume relationship for gases: P1 * V1 = P2 * V2 (this is basically your combined gas law  (P1*V1)/T1 = (P2*V2)/T2  but ignoring temperature since temperature is not changing here). Then the question tells you V2 is V1 decreased by 33%, or 1/3, meaning that V2 = 2/3 * V1.
Now let's plug in and simplify. P1 * V1 = P2 * 2/3 V1
The V1s cancel out on each side so P1 = P2 * 2/3
Then just solve for P2: P2 = 3/2 P1
I hope that helps!
For this one, remember Boyle's Law which tells us the pressurevolume relationship for gases: P1 * V1 = P2 * V2 (this is basically your combined gas law  (P1*V1)/T1 = (P2*V2)/T2  but ignoring temperature since temperature is not changing here). Then the question tells you V2 is V1 decreased by 33%, or 1/3, meaning that V2 = 2/3 * V1.
Now let's plug in and simplify. P1 * V1 = P2 * 2/3 V1
The V1s cancel out on each side so P1 = P2 * 2/3
Then just solve for P2: P2 = 3/2 P1
I hope that helps!