Calculating Net Force of a Helium Balloon in Thermodynamics - Tips and Tricks

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To calculate the net force of a helium balloon, it's essential to consider both the mass of the balloon's container and the mass of the helium inside. The buoyant force is determined by the air density, gravitational acceleration, and the balloon's volume, which was calculated to be 523.6 m^3. Initially, the user neglected the mass of the helium, leading to an incorrect total mass of 226.768 kg. Once this mass was included in the calculations, the user successfully reached the correct acceleration of 16.5 m/s^2. Accurate mass calculations are crucial for determining net force in thermodynamic scenarios involving buoyancy.
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OK, I have been working on this for a while.

I have a balloon, filled with helium.
mass = 140 kg
density(air) = 1.16 kg/m^3
density(He) = 1/7*density(air)
diameter of balloon = 10 m
bouyant force = density(air)*g*Volume(balloon)
weight = m*g
net force = bouyant force - weight = ma

I need to solve for a. The book tells the answer (16.5 m/s^2), so I know what I need to get to, but doing the steps above, I haven't gotten close.

Anybody have any ideas to help out?

Thanks!
 
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You need the mass of the 'entire' balloon, that is, the mass of the container itself which is 140 kg, plus the mass of the helium inside. I think that's about the only point where it can really go wrong.
Why don't you post what you got for the volume and mass of the balloon and what you got for the bouyancy.
 
ok, volume was 523.6 m^3, mass ended up being 226.768 kg.

i had forgot the mass of the helium, i got the right answer now, thanks!
 

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