How many helium-filled balloons would it take to lift a house off the ground, like in the Pixar movie Up?

Question

Assume the house has a mass of 55,000 kg and that each helium-filled balloon is spherical with a diameter of 33 cm.

Answer 1

He gas is 0.178 kg/m^3, air is 1.2kg/m^3 at T=20 celcius.

The weight he can list with volume V is V*(1.2-0.178)=1.022V

To lift 55000kg house, the V=55000/1.022=53800 m^3 He.

One balloon has 4*pi/3*(1/3)^3 m^3 he.

number of balloons needed are 53800* 81/4/pi=346782