Hot air is less dense than cool air, so hot air will rise above cool air. Increasing the air temperature inside a
hot air balloon makes it lighter than the surrounding air, so the balloon can lift up. The density of hot air is
about 0.25 kg/m less than that of cool air, which means a cubic meter of hot air can lift about 0.25 kg.
What is the minimum volume of hot air needed to lift a hot air balloon carrying 800 kg?