[babygene]

Where are your numbers? Ir;s been more than 1 hour...

[dragnet2]

There still crunching the numbers.

[AFPhys]

got distracted...

[spunkets]

1 mole of gas =22.4l at atmospheric pressure.

The molecular weight of N₂ is 28g/mole.

For O₂ it's 32g/mole.

The atmosphere is 20% oxygen and since it's Thursday, the rest of the minor components are on vacation, so...

0.8*28+0.2*32="molecular weight" of air = 28.4g/22.4l = 1.29g/l

The balloon contains He, with an atomic weight of 4.

4g/22.4l = 0.179g/l

The An object in a fluid is bouyed up by a force equal to the weight of the fluid displaced.

The balloon has a radius of 10ft and a height of 5ft. The volume is:

3.14*10*10*5 = 1570ft³.

1"=2.54cm, so...

12"/ft=12/ft*2.54cm = 30.5cm/

1ft³=30.5³ = 28317cm³/ft³

28317cm³/ft³ / 1000cm³/l = 28.3 l/ft³

28.3 l/ft³ * 1570ft³ =44431 l

44431*l * 1.29g = 57316g/(air displaced by balloon)

57316g/ 454g/lb = 126lbs of air displaced by the balloon.

The weight of the helium is:

0.179g/l * 44431*l / 454g/l = 17.5lbs

So...

126 - 17.5 = 109lbs of lift.