Lifting force on balloons

1. Sep 10, 2015

Drizzy

1. The problem statement, all variables and given/known data

Mr Bean – Mind the baby (19:45)

In the film we see how Mr. Bean air puts a stroller with a baby in with the help of a number of helium-filled balloons. Appreciate the reasonableness of this!

1. What is the density of helium and air?

2. What do you think a stroller with a baby should weigh?

3. How big is the lifting power of the balloon in the film?

4. How many balloons are using Mr. Bean?

5. How many balloons should be required?

2. Relevant equations
3. The attempt at a solution

1. The density of air at sea level and at 15 °C is 1.225 kg/m3. The density of helium is 178.6 g/cm3.

2. The weigh of the baby and the stroller is probably around 10*g

3. The lifting power of the ballon is: F=rho * g * V

Now I need the volume of the balloon, I can either estimate the volume or estimate the mass and then multiply it by the density to get the volume. What should I do?

4. I couldn't really count but he probably used around 20 balloons.

5. I divide the lifting foorce with the number of balloons that he used to see how much one balloon can lift. Then I calculate the difference between the lifting force and the stroller + baby's weight. so on...

Am I right?

2. Sep 10, 2015

SteamKing

Staff Emeritus
What source did you use to obtain the density of helium?

Don't you think it would be better if the densities of air and helium were expressed in the same units?

What are the units of "10*g"? What does that even mean?

3. Sep 10, 2015

Drizzy

I used wikipedia :P

Probably... 1.225 kg/m3. The density of helium is 178600 kg/m3.

g=9.82 and the mass of the storller+the baby is 10kg

4. Sep 10, 2015

SteamKing

Staff Emeritus
Do you really think that helium gas has a density of 178.6 tons per cubic meter? Wouldn't that make helium the most dense material on earth?

Either quote the mass of the stroller, 10 kg, or its weight, 98.2 N, but avoid expressions like "10*g".

5. Sep 10, 2015

Drizzy

oops it is 0.1786 kg/m3