Quiz - Physics - Displacement

[Pedro Burrito]

From the PADI Dive Theory Exam:

If an object that weighs 85 kg/187 pounds is neutrally buoyant in salt water, what is the volume of water the object displaces?

You will need to look at the constants to help with the answer: Constants Used For the Dive Theory Exam

I will post a daily question from my exams to help newer divers and to encourage more experienced divers to interact gracefully and helpfully with the newer divers.

Reminder - this is a post in the Basic Forum and it is a green zone. Please be nice and on topic.

Thank you for your patience while we try to give people something to discuss other than Covid-19 and/or Politics. I will post the answer covered by the spoiler tag later today.

 

[BrackaFish]

From the PADI Dive Theory Exam:

If an object that weighs 85 kg/187 pounds is neutrally buoyant in salt water, what is the volume of water the object displaces?

You will need to look at the constants to help with the answer: Constants Used For the Dive Theory Exam

I will post a daily question from my exams to help newer divers and to encourage more experienced divers to interact gracefully and helpfully with the newer divers.

Reminder - this is a post in the Basic Forum and it is a green zone. Please be nice and on topic.

Thank you for your patience while we try to give people something to discuss other than Covid-19 and/or Politics. I will post the answer covered by the spoiler tag later today.

Thanks for posting these questions as they go well with morning coffee

 

[jonhall]

EUREKA!! I don't think I have it!!

Is the correct combination - liter/cubic feet - a choice above? Without giving anything away and due to the fact I must be missing something, I seem to come up with an answer that has a part of the correct answer in two different choices above.

I feel like I need to get in a large graduated cylinder of salt water to know for sure!!

 

[BlueTrin]

EUREKA!! I don't think I have it!!

Is the correct combination - liter/cubic feet - a choice above? Without giving anything away and due to the fact I must be missing something, I seem to come up with an answer that has a part of the correct answer in two different choices above.

I feel like I need to get in a large graduated cylinder of salt water to know for sure!!

I believe the correct answer it there.

I obtained the number of litres then converted this figure in cubic feet.

 

[scubadada]

Thanks for posting these questions as they go well with morning coffee

Me too

 

[rhwestfall]

If neutrally buoyant, an object displaces a volume equivalent to it's weight.

keep it simple: 187# / 64 #/cf = XXX cf

 

[HKGuns]

The key is neutrally buoyant, so the volume of displacement will be something less than the volume of the object. You can pretty much reason your way to the correct answer knowing a little physics. (Assuming I chose the correct answer of course.)

BTW: Thanks for posting these, I find them far more interesting than Politics or the Virus and cancelled travel talk.

 

[TMHeimer]

Hey, think I got it right because I remember the weight of a cubic foot of sw without checking the constants list. Guess reviewing the manuals regularly does pay off....Now watch, I'll be wrong.
OK I got it wrong. I tried to just do it in my head without the calculator and ignored the obviously wrong answer in liters (still not good with that aspect of metric after 43 years up here....). But I'm great with kilometers & Celsius!
I picked the one with 3 cubic feet and it was 2.9. But hey, I understand it.

 

[MargaritaMike]

If neutrally buoyant, an object displaces a volume equivalent to it's weight.

keep it simple:

I think part of the challenge of the question is to look up the way to get the answer. He already gave us the constants. Hopefully people can make the correlation that the "object" is a human.

Cheers,
M²

 

[Brett Hatch]

Knowing that 1l of fresh water weighs 1kg, an 85kg object neutrally buoyant in fresh water would displace 85l of water. Knowing that salt water is "conventionally" 3% denser than salt water, we would expect a neutral object to displace 3% less salt water than it would fresh water.

Spoiler: math w/ answer

(85kg) / (1.03 kg/l) ~= 82.5l