The fire rises - hot air balloon · Physics Brawl 2015 #FoL.9

Physics · thermodynamics

Problem

What is the lowest temperature of the air (in °C) inside a balloon, which will make it float? The volume of the balloon is

V = 6\cdot10^6\text{l}

and its weight (without the air inside) is

m = 700\text{kg}

. The density of surrounding air is

\rho = 1.2\text{kg}\cdot\text{m}^{-3}

and the atmospheric pressure is

p = 101\text{kPa}