a hot air balloon is a sphere of radius 8 m. the air inside is at a temperature of 60° C. how large a mass can the balloon lift when the outside temperature is 20° C? (Assume air is an ideal gas R= 8.314 Jmole ⁻¹ K⁻¹, 1atm. = 1.013 x 10⁵ Pa. the membrane tension is 5 Nm⁻¹