They're fairly similar methinks but i just can't seem to get them.

Question 1)

A spherical balloon is inflated to a diameter of 32.0 cm. Assume that the gas in the balloon is of atmospheric pressure (101.3 kPa) and is at a temperature of 20.0*C. It is then taken by a diver 10.0 m under the sea. The temperature of the seawater at this depth is 17.0*C. Assuming the gas in the balloon is in thermal equilibrium with seawater, what is the volume of the balloon now?

Density of seawater = 1030.0 kg m–3
Acceleration due to gravity = 9.8 m s–2
Universal gas constant = 8.314 J mol–1 K–1

Question 2)
The mass of a hot air balloon and its cargo (not including the air inside) is 200kg. The air outside is at 10.0*C and 101kPa. The volume of the balloon is 400m^3. To what temperature must the air in the balloon be heated before the balloon will lift off? (Air density at 10.0*C is 1.25kg/m^3.)

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Sinisa Rules all.

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That is part of the reason that the mafia does so much drug trafficing, its so they wont die of hunger because they dont have anything.
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They're fairly similar methinks but i just can't seem to get them.

Question 1)

A spherical balloon is inflated to a diameter of 32.0 cm. Assume that the gas in the balloon is of atmospheric pressure (101.3 kPa) and is at a temperature of 20.0*C. It is then taken by a diver 10.0 m under the sea. The temperature of the seawater at this depth is 17.0*C. Assuming the gas in the balloon is in thermal equilibrium with seawater, what is the volume of the balloon now?

Density of seawater = 1030.0 kg m–3
Acceleration due to gravity = 9.8 m s–2
Universal gas constant = 8.314 J mol–1 K–1

Question 2)
The mass of a hot air balloon and its cargo (not including the air inside) is 200kg. The air outside is at 10.0*C and 101kPa. The volume of the balloon is 400m^3. To what temperature must the air in the balloon be heated before the balloon will lift off? (Air density at 10.0*C is 1.25kg/m^3.)

Its 1:40 am so I might get the equations wrong. Use p1v1/t1 = p2v2/t2 for the first one.

The second one... I could figure it out if I didnt want to sleep!
Sat in a lab, curing diseases. They actually LET me play with chemicals!
Quote by Guitardude19
Its 1:40 am so I might get the equations wrong. Use p1v1/t1 = p2v2/t2 for the first one.

The second one... I could figure it out if I didnt want to sleep!

I tried that but was wrong
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Sinisa Rules all.

Quote by zbest
That is part of the reason that the mafia does so much drug trafficing, its so they wont die of hunger because they dont have anything.
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I tried that but was wrong

Crap!

Well... Yakult should know, he is the physicist...

PM him or something, or post in the science thread... Someone will answer in that.
Sat in a lab, curing diseases. They actually LET me play with chemicals!
WAHEY! Late night physics! Give me a min, I'm just eating a lolly

(it's shaped like a rocket)
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h/o, getting to it

EDIT: shit, I'm really sorry, but I'm gonna have to do my own physics work at the moment. I'd love to help you out but I have to finish my own work first =[
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Last edited by vintage x metal at Mar 23, 2008,
Use (P1*V1) / T1 = (P2*V2) / T2

We don't know what P2 is though!

using P = Patm + (density of fluid)*(gravitational acceleration)*(depth) we do! The rest is just plugging in the numbers.

Next question:

Use Archimede's principle

F(buoyant) = ( (density of fluid / air ) * (gravitational accel. ) * volume ) + (mass of cargo)*(gravitational accel. )

Would you be able to do it now? Let me know if you have any other problems!

EDIT: Thank the lord for my meticulous revision note-making in the first year! Shame my second year notes are sh*t
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Quote by Yakult
Use (P1*V1) / T1 = (P2*V2) / T2

We don't know what P2 is though!

using P = Patm + (density of fluid)*(gravitational acceleration)*(depth) we do! The rest is just plugging in the numbers.

Next question:

Use Archimede's principle

F(buoyant) = ( (density of fluid / air ) * (gravitational accel. ) * volume ) + (mass of cargo)*(gravitational accel. )

Would you be able to do it now? Let me know if you have any other problems!

EDIT: Thank the lord for my meticulous revision note-making in the first year! Shame my second year notes are sh*t

The man is right. Go physicists.

Yakult, you studying physics or graduated or something?
Quote by ZanasCross
The man is right. Go physicists.

Yakult, you studying physics or graduated or something?

I'm halfway through my second year of 'uni doing physics with astrophysics. It's getting ridiculously hard

Nerd-five on the Heisenburg's uncertainty user title!

Are you studying physics too?
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I'm halfway through my second year of 'uni doing physics with astrophysics. It's getting ridiculously hard

Nerd-five on the Heisenburg's uncertainty user title!

Are you studying physics too?

Yeah, I'm in my third year. Right now I'm almost through quantum mechanics and basic Modern Theory (Special and Gen. relativity and whatnot) Doing a thesis on Chaos Theory and its effects on a half forced half unforced double pendulum. Lot of mechanics and whatnot, hoping to get on as an experimentalist with NASA over the summer.
Quote by ZanasCross
Yeah, I'm in my third year. Right now I'm almost through quantum mechanics and basic Modern Theory (relativity and whatnot) Doing a thesis on Chaos Theory and its effects on a half forced half unforced double pendulum. Lot of mechanics and whatnot, hoping to get on as an experimentalist with NASA over the summer.

Ahh, I do loads of quantum and relativity / classical mechanics. We've only touched on Chaos Theory at the moment, but our lecturer's promised that we'll be delving deeper next term... I can't say I'm excited

You know it's not a good sign when, two weeks into your Easter break, you can hardly remember what modules you're taking

Erm... I'm doing "Relativity, Vectors and Classical Mechanics", "Observing the Universe", "Electrodynamics" and "Optics" this semester. Optics is alright, Observing the Universe is genuinely interesting. The other two are just math *****s. I am seriously fed up of constantly switching coordinate systems and div / curl because I'm crap at it
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Quote by sinisa
They're fairly similar methinks but i just can't seem to get them.
Yeah, they're similar because they're both bullshit. To get the "answers" you have to ignore part of reality. The real answers will be somewhat different from the solutions you find.

Still, they do serve somewhat of a purpose. They allow you to get a rough idea by applying some of the principals you're studying.

Quote by sinisa
Question 1)

A spherical balloon is inflated to a diameter of 32.0 cm. Assume that the gas in the balloon is of atmospheric pressure (101.3 kPa) and is at a temperature of 20.0*C. It is then taken by a diver 10.0 m under the sea. The temperature of the seawater at this depth is 17.0*C. Assuming the gas in the balloon is in thermal equilibrium with seawater, what is the volume of the balloon now?

Density of seawater = 1030.0 kg m–3
Acceleration due to gravity = 9.8 m s–2
Universal gas constant = 8.314 J mol–1 K–1
Here you have to ignore the force of the balloon acting on the gas inside. Just focus on the number of molecules that are present according to the pressure, temperature, and volume when the balloon is inflated. Then determine the pressure that the same number of molecules would exert on the seawater of equivalent volume at the new temperature and depth. That's the new volume of the balloon. It completely ignores the force of the balloon (which will be greater at a smaller volume -- non-linear coefficient, but that's a whole different subject).

Quote by sinisa
Question 2)
The mass of a hot air balloon and its cargo (not including the air inside) is 200kg. The air outside is at 10.0*C and 101kPa. The volume of the balloon is 400m^3. To what temperature must the air in the balloon be heated before the balloon will lift off? (Air density at 10.0*C is 1.25kg/m^3.)

Here you have a fixed volume, the volume of the balloon. You're given the mass of the balloon and the cargo. But not the volume of the cargo. So you're expected to ignore that.

Just determine the mass of the air of the same volume as the balloon, subtract the mass of the balloon and cargo. That tells you the mass of the air that must occupy the volume of the balloon. If you know the mass and the volume (and pressure, because the pressure inside and out must be equal), you can determine the temperature that number of molecules must be at to fill that volume.

Since the total mass of the air now in the balloon, mass of the balloon, and the mass of the cargo are equal to the mass of the air they displace, they are at neutral buoyancy. One less molecule of air in the balloon, and the balloon will begin to rise.

The error in this, is that we ignored the volume of air that was displaced by the cargo. The balloon has long since risen. The solution is a failure, but you do the best you can with the information given.
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Use (P1*V1) / T1 = (P2*V2) / T2

We don't know what P2 is though!

using P = Patm + (density of fluid)*(gravitational acceleration)*(depth) we do! The rest is just plugging in the numbers.

Next question:

Use Archimede's principle

F(buoyant) = ( (density of fluid / air ) * (gravitational accel. ) * volume ) + (mass of cargo)*(gravitational accel. )

Would you be able to do it now? Let me know if you have any other problems!

EDIT: Thank the lord for my meticulous revision note-making in the first year! Shame my second year notes are sh*t

Genius. Thank you so much P2 in Q1 was the one giving me problems, i forgot to take into account density*g*d so ended up assuming pressure was kept constant I got the answer now though, thanks again!

But with Q2 my problem was not in finding the force necessary to lift the balloon, but by how much does the pressure need to increase inside the balloon to exert this pressure? And then, in turn, find out by how much does the temperature need to be raised to raise the pressure by the amount necessary.

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Ummm at uni we don't have homework. We have to figure out things for ourselves, and when the lecturer/tutor/lab instructor is away on an Easter holiday, and when my brother (compsci grad /w postgrad diploma) can't figure it out, and when the stupid book and online revision thing don't have working to explain the solution, i have to go elsewhere to find the method now don't i?

Enter The Pit.
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Sinisa Rules all.

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That is part of the reason that the mafia does so much drug trafficing, its so they wont die of hunger because they dont have anything.
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Yeah, they're similar because they're both bullshit. To get the "answers" you have to ignore part of reality. The real answers will be somewhat different from the solutions you find.

Still, they do serve somewhat of a purpose. They allow you to get a rough idea by applying some of the principals you're studying.

Here you have to ignore the force of the balloon acting on the gas inside. Just focus on the number of molecules that are present according to the pressure, temperature, and volume when the balloon is inflated. Then determine the pressure that the same number of molecules would exert on the seawater of equivalent volume at the new temperature and depth. That's the new volume of the balloon. It completely ignores the force of the balloon (which will be greater at a smaller volume -- non-linear coefficient, but that's a whole different subject).

Here you have a fixed volume, the volume of the balloon. You're given the mass of the balloon and the cargo. But not the volume of the cargo. So you're expected to ignore that.

Just determine the mass of the air of the same volume as the balloon, subtract the mass of the balloon and cargo. That tells you the mass of the air that must occupy the volume of the balloon. If you know the mass and the volume (and pressure, because the pressure inside and out must be equal), you can determine the temperature that number of molecules must be at to fill that volume.

Since the total mass of the air now in the balloon, mass of the balloon, and the mass of the cargo are equal to the mass of the air they displace, they are at neutral buoyancy. One less molecule of air in the balloon, and the balloon will begin to rise.

The error in this, is that we ignored the volume of air that was displaced by the cargo. The balloon has long since risen. The solution is a failure, but you do the best you can with the information given.

At first glance, i thought you were way overthinking. But i have a few questions:

In Q1, the number of molecules remains constant. I don't see where it comes into it? When you say "Then determine the pressure that the same number of molecules would exert on the seawater of equivalent volume at the new temperature and depth. That's the new volume of the balloon." Could you please elaborate on that point?

In Q2, what do you mean when you say "Just determine the mass of the air of the same volume as the balloon, subtract the mass of the balloon and cargo. That tells you the mass of the air that must occupy the volume of the balloon."

The air inside and outside the balloon initially has equal density. The mass of the air inside is 1.25*400 = 500kg. The mass of the cargo (yes we assume it's a point mass) is 200kg. So, according to what i understand from your statement just above, 500 - 200 = 300kg which is the mass of the air that must occupy the volume of the balloon?

I thought volume was being kept constant?
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That is part of the reason that the mafia does so much drug trafficing, its so they wont die of hunger because they dont have anything.
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Here I was thinking I was awesome because we're doing work based on MAX PLANCK, PHYSICS EXTRAORDINAIRE.

Y'know, E=hf and all that. Cool stuff

1. Why did you bold the words "Max Planck, Physics extraordinaire?"
2. Do you think throwing out an equation makes you look cool?
3. Yeah, it is cool stuff.
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while were on homework... good intro for an essay on the Russian Revolution?

On July 16,1918 the Romanov’s ,royal family of Russia, are shot ,cut up ,burned, poured acid on ,and their ashes are scattered throughout Russia (Suares 180). These murders were brought on by the Russian Revolution of 1917. This revolution was the most brutal of the twentieth century and had a huge impact on modern history.
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while were on homework... good intro for an essay on the Russian Revolution?

On July 16,1918 the Romanov’s ,royal family of Russia, are shot ,cut up ,burned, poured acid on ,and their ashes are scattered throughout Russia (Suares 180). These murders were brought on by the Russian Revolution of 1917. This revolution was the most brutal of the twentieth century and had a huge impact on modern history.

Nah.

With the brutal deaths of the Romanov's, Russia's royal family, events that were to shape the course of modern history were already being instigated. From the withdrawl of Russia (pardon me, the USSR) from WWI, to the enormity of the USSR's Stalinist industrialization, to the events and causes of WWII, to sowing the seeds of the Cold War, the Russian Revolution truly did affect the course of the world in ways that could only be described as a complex interwining, and occasional juxtaposition of, seemingly innocuous events that, only when seen in light of each other and the larger socio-economic politic sphere, could the true effects be fathomed.

Ahem. If you look closely, you can see that it's only 2 sentences long. Short 'n' sweet
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Sinisa Rules all.

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That is part of the reason that the mafia does so much drug trafficing, its so they wont die of hunger because they dont have anything.
Before:

Quote by JaketheBaptist
On July 16,1918 the Romanov’s ,royal family of Russia, are shot ,cut up ,burned, poured acid on ,and their ashes are scattered throughout Russia (Suares 180). These murders were brought on by the Russian Revolution of 1917. This revolution was the most brutal of the twentieth century and had a huge impact on modern history.

After:

On July 16,1918, the Romanovs, the royal family of Russia, were shot, cut, and burned. The perpetrators poured acid on their remains and scattered their ashes throughout Russia (Suares 180). These murders were brought on by the Russian Revolution of 1917. This revolution was the one of the most brutal of the twentieth century and has had a huge impact on modern history.

I just fixed the improprieties in your punctuation, tense, and added a couple of words. Didn't mess with the actual information or write anything of my own.
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Last edited by darkstar2466 at Mar 23, 2008,
Quote by sinisa
Nah.

With the brutal deaths of the Romanov's, Russia's royal family, events that were to shape the course of modern history were already being instigated. From the withdrawl of Russia (pardon me, the USSR) from WWI, to the enormity of the USSR's Stalinist industrialization, to the events and causes of WWII, to sowing the seeds of the Cold War, the Russian Revolution truly did affect the course of the world in ways that could only be described as a complex interwining, and occasional juxtaposition of, seemingly innocuous events that, only when seen in light of each other and the larger socio-economic politic sphere, could the true effects be fathomed.

Ahem. If you look closely, you can see that it's only 2 sentences long. Short 'n' sweet

maybe i should combine?

using a lot of big words right off the bat usualy gets them too
Last edited by JaketheBaptist at Mar 24, 2008,
Quote by JaketheBaptist
maybe i should combine?

using a lot of big words right off the bat usualy gets them too

Well yea. C'mon dude, i used "Stalinist industrialization," "complex interwining," "occasional juxtaposition," "seemingly innocuous," "socio-economic politic sphere," "fathomed," and a bit of alliteration with "sowing the seeds" all in the same sentence. That's gotta get you some credit.

My question/thread's getting hijacked isn't it?
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That is part of the reason that the mafia does so much drug trafficing, its so they wont die of hunger because they dont have anything.
official homework thread??? yeah once i wrote a report that was **** other then the intro and got an A on it
Wow, I just feel like a geek after reading and understanding all of this stuff, a year ago I'd probably be scratching my head.