Answer
$T2=83.7°C$
Work Step by Step
For ideal gases:
$PV=mRT$
Given $P_1=500\ kPa, V_1=1\ m³, T_{1,He}=40°C, T_{1,N_2}=120°C$,
$R_{N_2}=0.2968 kJ/kg.K,\ R_{He}=2.0769 kJ/kg.K$
solving for the masses we get:
$m_{N_2}=4.287 kg, m_{He}=0.7691 kg$
The energy balance for the system is:
$\Delta U_{N_2}+\Delta U_{He}+\Delta U_{Cu}=0$
With $c_{v,N_2}=0.743 kJ/kg.K, c_{v,He}=3.1156 kJ/kg.K, c_{v,Cu}=0.386\ kJ/kg.K$,
$m_{Cu}=8\ kg, T_{1,Cu}=80°C$:
solving for the final temperature:
$T2=83.7°C$
