Question

A blimp typically contains about 5400 m3 of helium. Suppose the helium's pressure and temperature are 1.3×10⁵ Pa and 18 ∘C , respectively.

a)What's the mass of helium in the blimp?

Express your answer using two significant figures and include the appropriate units.

b)

What's the buoyant force on the blimp?

Express your answer using two significant figures and include the appropriate units.

c)

What's the maximum possible mass for the rest of the blimp (skin and payload) if it's neutrally buoyant (neither rising nor sinking)?

Express your answer using two significant figures and include the appropriate units.

**Please answer all parts, will be greatly appreciated!**

Answer 1

Use the perfect gas law to find the number of moles, n:

PV = n R T

n = PV/RT

= (1.3 x 10^5 Pa x 5400m^3)/(8.314 x 291)    [T = 18+273 K = 291K]

= 290157.7 moles

Each mole has a mass of 4 g or 0.004kg, so the total mass of He is

290157.7 mole x 0.004kg/mole =

1160.6 kg = 1200 kg (2 sf)

b)

Buoyant force F_B = weight

= mg = 1160.6 x 9.8

= 11374 N = 11000 N (2 sf)

c)

Density of He: rho = 0.164 kg/m3

mass = rho x V

= 0.164 x 5400

= 885.6

Maximum possible mass for the rest of the blimp

= 1160.6 – 885.6

= 275 kg = 280 kg (2 sf)