Question

On a cold, 5°F day, the nosewheel tire of a Learjet, having an internal volume of 1000. in3 is inflated to 30 psi (i.e., 30 lb/in2) above the ambient pressure of 14.7 psi. Calculate the weight (in pounds) and specific volume of the air in the tire. (Be careful of units here--we usually use feet, not inches, with imperial units in this course, and you need to work with absolute temperatures.)

Answer 1

Answer:

The weight in (pounds ) is $m = 0.14994 \ lb$

The specific volume is $V_s = 0.2403 \ m^3 /kg$

Explanation:

From the question we are told that

The temperature is $T = 5^o F = (5^oF - 32) * \frac{5}{9} = -15 ^oC + 273 = 258 K$

The volume is $V = 1000 \ in^3 = \frac{1000}{1728} = 0.5787 ft^3 = 0.0164\ m^3$

The initial absolute pressure is $P = 30\ lb/in^2 = 30\ lb/in^2 * \frac{1}{ \frac{in^2}{144ft^2} } = 4320 \ lb/ft^2 = 308 .19 KPa$

Generally from ideal gas equation we have

$P * V = m RT$

Here m is the weight nose wheel tire in pounds

R is the gas constant of air with value $R = 0.287 \ \frac{KJ}{kg\cdot K}$

So

$308 .19 * 0.0164 = m * 0.287* 258$

=> $m = 0.068 \ kg$

Converting to pounds

$m = 0.068 * 2.205$

$m = 0.14994 \ lb$

Form this equation $P * V = m RT$ specific volume is

$\frac{V}{m} = \frac{RT}{ P}$

=>    $V_s = \frac{V}{m} = \frac{0.287 * 258 }{308 .19 }$

=> $V_s = 0.2403 \ m^3 /kg$