How Do You Calculate the Buoyant Force for a Stratospheric Balloon?

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To calculate the buoyant force for a stratospheric balloon, the formula involves the total weight of the balloon, payload, and helium, balanced by the buoyant force and acceleration. The buoyant force can be determined using Archimedes' Principle, which states that it equals the weight of the fluid displaced by the balloon. The discussion emphasizes that to find the buoyant force, one must calculate the mass of the displaced fluid using the formula rho = m/v, and then multiply by the acceleration due to gravity (g = 9.8 m/s²). Understanding the relationship between volume and weight is crucial, as volume alone does not equate to force. This approach aids in accurately determining the buoyant force acting on the balloon.
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Homework Statement
The figure on the right shows a stratospheric balloon
carrying a payload. The density of helium at 1.0 atm and 15 oC
is 0.168 kg/m3 and the density for air is 1.225 kg/m3. The mass
of the balloon (skin without helium) and the payload is 260 kg.
The volume of the balloon at ground level is 300 m3
Relevant Equations
Upthrust?
I have gathered the formula:
F(Bouyant force) - (Mballoon + Mpayload)g - (Mhelium)g = (Mballoon + Mhelium + Mpayload)a
But i can't seem to figure out what is the buoyant force to find a. Or am i mistaking something?

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nicky670 said:
F(Bouyant force) - (Mballoon + Mpayload)g - (Mhelium)g = (Mballoon + Mhelium + Mpayload)a
Ok
But i can't seem to figure out what is the buoyant force to find a. Or am i mistaking something?
Have you covered Archimedes' Principle?
 
Yes i have.
 
According to Archimedes' principle, how would you find the buoyant force on a rock of volume V that is completely submerged in water?
 
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it is the volume of water displaced by the rock that will get you the buoyant force right?
TSny said:
According to Archimedes' principle, how would you find the buoyant force on a rock of volume V that is completely submerged in water?
It will be the volume of water displaced by the rock right? For buoyant force
 
nicky670 said:
it is the volume of water displaced by the rock that will get you the buoyant force right?

It will be the volume of water displaced by the rock right? For buoyant force
A volume is not a force. What attribute of that volume of fluid?
 
haruspex said:
A volume is not a force. What attribute of that volume of fluid?
The weight of the volume of water displaced
 
nicky670 said:
The weight of the volume of water displaced
Yes, that's right. Does this help with finding the buoyant force on the balloon?
 
TSny said:
Yes, that's right. Does this help with finding the buoyant force on the balloon?
So i use rho = m/v formula to find the mass and then multiply by g=9.8 to get the weight?
 
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nicky670 said:
So i use rho = m/v formula to find the mass and then multiply by g=9.8 to get the weight?
That's the right idea. For what substance are you going to find the mass in order to get the buoyant force?
 

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