Answer:
1.05045 kg/m³
Explanation:
[tex]\rho_a[/tex] = Density of air = 1.26 kg/m³
[tex]\rho_{ha}[/tex] = Density of hot air
[tex]m_a[/tex] = Mass of balloon = 539 kg
g = Acceleration due to gravity = 9.81 m/s²
v = Volume of air in balloon = [tex]2.62\times 10^3\ m^3[/tex]
The net force on the balloon will be
[tex]F_n=(\rho_a-\rho_{ha})vg[/tex]
Also
[tex]F_n=m_ag[/tex]
[tex]\\\Rightarrow 549g=(\rho_a-\rho_{ha})vg\\\Rightarrow 549=(1.26-\rho_{ha})2.62\times 10^3\\\Rightarrow -\rho_{ha}=\frac{549}{2.62\times 10^3}-1.26\\\Rightarrow \rho_{ha}=1.05045\ kg/m^3[/tex]
The density of hot air inside the envelope is 1.05045 kg/m³