Answer
a) $\Delta U=1645\ MJ$
b) $\Delta U=626.4\ MJ$
c) $\Delta U=400.0\ MJ$
Work Step by Step
a) Assuming only phase-change heat:
$\Delta U=V.\Delta \hat{h}_v$
Given $V=5000L,\ \hat{h}_v=329\ kJ/L$:
$\Delta U=1645\ MJ$
b)$\Delta U=mc_v\Delta T=\rho Vc_v\Delta T$
Given $V=5\ m³,\ \rho=2700\ kg/m³,\ c_v=2.32\ kJ/kg.°C,\ \Delta T=20°C$:
$\Delta U=626.4\ MJ$
c) b)$\Delta U=mc_v\Delta T=\rho Vc_v\Delta T$
Given $V=5\ m³,\ \rho=1000\ kg/m³,\ c_v=4.0\ kJ/kg.°C,\ \Delta T=20°C$:
$\Delta U=400.0\ MJ$
