Quiz - Physics - Fill a Container at 40 metres/132 feet

[saxman242]

do you mind me asking what size bag would a 7ltr cylinder at 200bar fill at the same depth and can you show how you got the answer

Roughly 276l.

P1V1=P2V2

P1=200bar=197atm
V1=7l
P2=5 atm

V2=P1V1/P2=(197*7)/(5)=276l

 

[Celt]

Roughly 276l.

P1V1=P2V2

P1=200bar=197atm
V1=7l
P2=5 atm

V2=P1V1/P2=(197*7)/(5)=276l

Is p pressure and v volume

 

[BlueTrin]

Is p pressure and v volume

Yes, he is basically saying that the total quantity of gas stays the same.

When pressure increases then the volume decrease

 

[saxman242]

Is p pressure and v volume

Correct

 

[Celt]

Correct

thanks i tried it on a calculator and got 275.8. is there a way to calculate how much lift you could get, i have another question but i don't know how to put it. i think i have some photos and may be able to guess the sizes

 

[BlueTrin]

thanks i tried it on a calculator and got 275.8. is there a way to calculate how much lift you could get, i have another question but i don't know how to put it. i think i have some photos and may be able to guess the sizes

You can compute the buoyant force but if you want to know how much you can lift with it, you should just know that the whole system (the container of gas and what you are trying to lift) will be in equilibrium when it has the same weight than equivalent volume of liquid.

Anything lighter will float.

 

[saxman242]

Just a rounding difference at that point.

A 276 liter lift bag would have a lift capacity of about 276 kg (assuming the bag and air themselves are negligible mass, which isn't true. Lift bags in that size range seem to weigh roughly 5-10 kg, so let's call it 265 kg for good measure). That'd require you to have a lift bag with a 276 liter capacity though, which is fairly decent size.

 

[Celt]

Just a rounding difference at that point.

A 276 liter lift bag would have a lift capacity of about 276 kg (assuming the bag and air themselves are negligible mass, which isn't true. Lift bags in that size range seem to weigh roughly 5-10 kg, so let's call it 265 kg for good measure). That'd require you to have a lift bag with a 276 liter capacity though, which is fairly decent size.

I’m wondering what I would need to fill 2 1 ton bags which brings me nicely to the next question. If a tank measured 5 feet by 2 feet by 5 feet deep and was 1/2 inch thick bronze and the bottom of the tank had a 4 inch copper coil what kind of weight could you expect, I have photos but don’t know how to load them

 

[saxman242]

I’m wondering what I would need to fill 2 1 ton bags which brings me nicely to the next question.

2 1 ton bags would require about 1800 liters of displacement. If you're starting with tanks at 200 bar and you need to fill the bags at 40 meters depth, you'd need ~6.5 7 liter tanks.

 

[Celt]

2 1 ton bags would require about 1800 liters of displacement. If you're starting with tanks at 200 bar and you need to fill the bags at 40 meters depth, you'd need ~6.5 7 liter tanks.

I’d be hoping to have enough lift by half filling both bags which would be 1 ton so 2 15ltr tanks would be plenty, now all I have to figure is what the tank weights? Thanks very much for your reply