## Wednesday, May 13, 2009

### Bouyancy Problem

This should be too easy. We have on the pic 100 orange colored toy balloons supporting in suspension a man in the air. Each balloon weights 80 grams and contains 1.2 cubic meters of Helium. The weight of air at STP is 1.20 gr/l and the weight of helium 0.18 gr/l. What is the weight of the man? Dont try it at home.

Ronduck said...

Volume of balloons:
100 balloons*1.2m3=120 cubic meters

120m3*1000=120,000 liters

lift per liter:

1.20g-0.18g=1.02g/L

grams of lift:

1.02*120,000=122,400g

weight of balloons:
100 balloons*80g=8,000g

net lift:

122,400-8,000=114,400g

114,400/1,000=114.4 kg

since 1 kg = 2.2lbs then:

114.4*2.2 = 251.68 lbs.

Anonymous said...

Koko tells me , the key to this is to appreciate that the upward forces are balancing the downward ones.

But she demands more bananas before she will continue.

Anon.

J said...

Logical, Mr Ronduck. You should come to study engineering in the university in Ariel, in Samaria. Four years and you are entitled to design buildings.

Ronduck said...

No J, like you said...

This should be too easy.

This is a simple question, and I would be sure all but the graduates from Central Asia should be able to answer it correctly.