A plastic bag is filled with hydrogen at atmospheric pressure and 18.0 oC. Assum

Question

A plastic bag is filled with hydrogen at atmospheric pressure and 18.0 oC. Assume that the mass of the bag is negligible and take the temperature of the outside air to be 0 oC. With the help of this "balloon" we want to lift a 44.0 kg girl off her feet. How large a volume of hydrogen (in m3) is required? If hot air is used instead of hydrogen, what is the required volume of the balloon if the air inside can be maintained at 39.0 oC ?

Explanation / Answer

P = 1 atm Tin = 18 degC = 291 K Tout = 0 degC = 273 K m = 44 kg Let volume of air displaced = V from , PV = nRT We have , PM = d RT, Thus, density of H2 at 18 degC is d = (101.325 kPa x 2)/(8.315 x 291) = Thus the buoyancy force must be greater than mxg = 44 x 9.8 = 431.2 N B = (Density of air at 0 degC - density of H2 at 18 degC)xVxg => 431.2 = (1.32 kg/m3 - 0.08375 kg/m3) x V x 9.8 => V = 35.619 m3 For air, d at 0 degC = (101.325 x 28.964)/(8.315 x 273) = 1.32 kg/m3 For air at 39 degC d = (101.325 x 28.964)/(8.315 x 312) = 1.13 kg/m3 B = (1.32-1.13) x V x 9.8 = 44 x 9.8 => V = 231.579 m3

Related Questions

Navigate

• Browse (All)
• Browse A
• Subjects

---

---

Integrity-first tutoring: explanations and feedback only — we do not complete graded work. Learn more.