The densities of air, helium, and hydrogen (at p = 1.0 atm and T = 20°C) are 1.20 kg/m', 0.166 kg/m, and 0.0899 kg/m, respectively.
(a) What is the volume in cubic meters displaced by a hydrogen-filled airship that has a total "lift" of 120 kN? (The "lift" is the amount by which the buoyant force exceeds the weight of the gas that fills the airship.)
(b) What would be the "lift" if helium were used instead of hydrogen? In view of your answer, why is helium used in modern airships like advertising blimps?