Answer:
a.
which is constant therefore, n = constant
b. The temperature at the end of the process is 109.6°C
c. The work done by the balloon boundaries = 10.81 MJ
The work done on the surrounding atmospheric air = 10.6 MJ
Explanation:
p₁ = 100 kPa
T₁ = 27°C
D₁ = 10 m
v₂ = 1.2 × v₁
p ∝ α·D
α = Constant
![v_1 = \dfrac{4}{3} \times \pi \times r^3](https://tex.z-dn.net/?f=v_1%20%3D%20%5Cdfrac%7B4%7D%7B3%7D%20%5Ctimes%20%20%5Cpi%20%5Ctimes%20r%5E3)
![\therefore v_1 = \dfrac{4}{3} \times \pi \times \left (\dfrac{10}{2} \right )^3 = 523.6 \ m^3](https://tex.z-dn.net/?f=%5Ctherefore%20v_1%20%3D%20%5Cdfrac%7B4%7D%7B3%7D%20%5Ctimes%20%20%5Cpi%20%5Ctimes%20%20%5Cleft%20%28%5Cdfrac%7B10%7D%7B2%7D%20%20%5Cright%20%29%5E3%20%3D%20523.6%20%5C%20m%5E3)
v₂ = 1.2 × v₁ = 1.2 × 523.6 = 628.32 m³
Therefore, D₂ = 10.63 m
We check the following relation for a polytropic process;
We have;
![\dfrac{\alpha \times D_{1}}{\alpha \times D_{2}} = \left (\dfrac{ \dfrac{4}{3} \times \pi \times \left (\dfrac{D_2}{2} \right )^3}{\dfrac{4}{3} \times \pi \times \left (\dfrac{D_1}{2} \right )^3} \right )^{n} = \left (\dfrac{ \left{D_2} ^3}{ {D_1}^3} \right )^{n}](https://tex.z-dn.net/?f=%5Cdfrac%7B%5Calpha%20%5Ctimes%20D_%7B1%7D%7D%7B%5Calpha%20%5Ctimes%20D_%7B2%7D%7D%20%3D%20%5Cleft%20%28%5Cdfrac%7B%20%5Cdfrac%7B4%7D%7B3%7D%20%5Ctimes%20%20%5Cpi%20%5Ctimes%20%20%5Cleft%20%28%5Cdfrac%7BD_2%7D%7B2%7D%20%20%5Cright%20%29%5E3%7D%7B%5Cdfrac%7B4%7D%7B3%7D%20%5Ctimes%20%20%5Cpi%20%5Ctimes%20%20%5Cleft%20%28%5Cdfrac%7BD_1%7D%7B2%7D%20%20%5Cright%20%29%5E3%7D%20%20%20%5Cright%20%29%5E%7Bn%7D%20%3D%20%5Cleft%20%28%5Cdfrac%7B%20%20%20%5Cleft%7BD_2%7D%20%20%5E3%7D%7B%20%7BD_1%7D%5E3%7D%20%20%20%5Cright%20%29%5E%7Bn%7D)
![\dfrac{D_{1}}{ D_{2}} = \left (\dfrac{ \left{D_2} }{ {D_1}} \right )^{3\times n} = \left (\dfrac{ \left{D_1} }{ {D_2}} \right )^{-3\times n}](https://tex.z-dn.net/?f=%5Cdfrac%7BD_%7B1%7D%7D%7B%20D_%7B2%7D%7D%20%3D%20%5Cleft%20%28%5Cdfrac%7B%20%20%20%5Cleft%7BD_2%7D%20%20%7D%7B%20%7BD_1%7D%7D%20%20%20%5Cright%20%29%5E%7B3%5Ctimes%20n%7D%20%3D%20%20%5Cleft%20%28%5Cdfrac%7B%20%20%20%5Cleft%7BD_1%7D%20%20%7D%7B%20%7BD_2%7D%7D%20%20%20%5Cright%20%29%5E%7B-3%5Ctimes%20n%7D)
![\dfrac{ D_{1}}{ D_{2}} = \left ( 1.2 \right )^{n} = \left (\dfrac{ \left{D_2} ^3}{ {D_1}^3} \right )^{n}](https://tex.z-dn.net/?f=%5Cdfrac%7B%20D_%7B1%7D%7D%7B%20D_%7B2%7D%7D%20%3D%20%5Cleft%20%28%201.2%20%20%5Cright%20%29%5E%7Bn%7D%20%3D%20%5Cleft%20%28%5Cdfrac%7B%20%20%20%5Cleft%7BD_2%7D%20%20%5E3%7D%7B%20%7BD_1%7D%5E3%7D%20%20%20%5Cright%20%29%5E%7Bn%7D)
![log \left (\dfrac{D_{1}}{ D_{2}}\right ) = -3\times n \times log\left (\dfrac{ \left{D_1} }{ {D_2}} \right )](https://tex.z-dn.net/?f=log%20%20%5Cleft%20%28%5Cdfrac%7BD_%7B1%7D%7D%7B%20D_%7B2%7D%7D%5Cright%20%29%20%20%3D%20%20-3%5Ctimes%20n%20%5Ctimes%20log%5Cleft%20%28%5Cdfrac%7B%20%20%20%5Cleft%7BD_1%7D%20%20%7D%7B%20%7BD_2%7D%7D%20%20%20%5Cright%20%29)
n = -1/3
Therefore, the relation, pVⁿ = Constant
b. The temperature T₂ is found as follows;
![\left (\dfrac{628.32 }{523.6} \right )^{-\dfrac{1}{3} } = \left (\dfrac{300.15}{T_{2}} \right )^{\dfrac{-\dfrac{1}{3}}{-\dfrac{1}{3}-1}} = \left (\dfrac{300.15}{T_{2}} \right )^{\dfrac{1}{4}}](https://tex.z-dn.net/?f=%5Cleft%20%28%5Cdfrac%7B628.32%20%7D%7B523.6%7D%20%20%20%5Cright%20%29%5E%7B-%5Cdfrac%7B1%7D%7B3%7D%20%7D%20%3D%20%5Cleft%20%28%5Cdfrac%7B300.15%7D%7BT_%7B2%7D%7D%20%20%20%5Cright%20%29%5E%7B%5Cdfrac%7B-%5Cdfrac%7B1%7D%7B3%7D%7D%7B-%5Cdfrac%7B1%7D%7B3%7D-1%7D%7D%20%3D%20%5Cleft%20%28%5Cdfrac%7B300.15%7D%7BT_%7B2%7D%7D%20%20%20%5Cright%20%29%5E%7B%5Cdfrac%7B1%7D%7B4%7D%7D)
T₂ = 300.15/0.784 = 382.75 K = 109.6°C
c. ![W_{pdv} = \dfrac{p_1 \times v_1 -p_2 \times v_2 }{n-1}](https://tex.z-dn.net/?f=W_%7Bpdv%7D%20%3D%20%5Cdfrac%7Bp_1%20%5Ctimes%20v_1%20-p_2%20%5Ctimes%20v_2%20%7D%7Bn-1%7D)
![p_2 = \dfrac{p_{1}}{ \left (\dfrac{V_{2}}{V_{1}} \right )^{n} } = \dfrac{100\times 10^3}{ \left (1.2) \right ^{-\dfrac{1}{3} } }](https://tex.z-dn.net/?f=p_2%20%3D%20%5Cdfrac%7Bp_%7B1%7D%7D%7B%20%5Cleft%20%28%5Cdfrac%7BV_%7B2%7D%7D%7BV_%7B1%7D%7D%20%20%20%5Cright%20%29%5E%7Bn%7D%20%7D%20%3D%20%20%5Cdfrac%7B100%5Ctimes%2010%5E3%7D%7B%20%5Cleft%20%281.2%29%20%5Cright%20%20%5E%7B-%5Cdfrac%7B1%7D%7B3%7D%20%7D%20%7D)
p₂ = 100000/0.941 = 106.265 kPa
![W_{pdv} = \dfrac{100 \times 10^3 \times 523.6 -106.265 \times 10^3 \times 628.32 }{-\dfrac{1}{3} -1} = 10806697.1433 \ J](https://tex.z-dn.net/?f=W_%7Bpdv%7D%20%3D%20%5Cdfrac%7B100%20%5Ctimes%2010%5E3%20%5Ctimes%20523.6%20-106.265%20%5Ctimes%2010%5E3%20%20%5Ctimes%20628.32%20%7D%7B-%5Cdfrac%7B1%7D%7B3%7D%20-1%7D%20%3D%2010806697.1433%20%5C%20J)
The work done by the balloon boundaries = 10.81 MJ
Work done against atmospheric pressure, Pₐ, is given by the relation;
Pₐ × (V₂ - V₁) = 1.01×10⁵×(628.32 - 523.6) = 10576695.3 J
The work done on the surrounding atmospheric air = 10.6 MJ