# Find the radius of the balloon

1. Jul 13, 2010

### physics_freak

1. The problem statement, all variables and given/known data
Estimate the radius of a helium filled balloon if a load of 180 kg (including the weight of the empty balloon) is to be lifted. Density of helium is 0.179 kg/m^3

2. Relevant equations

F=rho*g*V

3. The attempt at a solution

F=$$\rho$$gV

r=3.22m

2. Jul 13, 2010

### Gear.0

I don't think it's that simple.
Don't you also need to know the density of air?

If this was done in a vacuum then no matter how big your radius was it would not float.

Also, from the way the problem is worded it doesn't sound like the weight of the helium is incorporated in the 180kg.
You can solve this if you are given the density of the surrounding fluid in which the balloon is to float (most likely normal air).

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