Find the buoyant force on a hot air balloon

1. Feb 6, 2010

PHart111

1. The problem statement, all variables and given/known data
I'm trying to find the buoyant force on a hot air balloon. The mass of the displaced fluid is 2800 kg and the acceleration is that of gravity, (let's say 10 m/s^2).

2. Relevant equations
F=ma

3. The attempt at a solution
I think that you can just multiply these together to find this, or do you have to subtract the weight of the hot air balloon from it as well.

Thank you

2. Feb 6, 2010

Spinnor

I think you are missing some information. A hot air balloon floats because the hot air inside the balloon is less dense the the surrounding air. I think we also need the temperature of the hot air in the balloon and the temperature of the air outside the balloon?

3. Feb 6, 2010

Staff: Mentor

What is the exact problem you are trying to solve? The buoyant force is the upward force exerted by the surrounding fluid (the air)--it has nothing to do with the weight of the balloon. If you want the net force on the balloon, then you'd need to subtract the weight of the balloon (and anything attached to it).

Per Archimedes's principle, the buoyant force equals the weight of the displaced fluid, which is its mass times g.