In a mixing chamber hot water enters at a temperature of $80^{\circ} \mathrm{C}$ with a flowrate of $0.5 \mathrm{~kg} / \mathrm{s}$. From another entry, cold water enters the chamber at $20^{\circ} \mathrm{C}$. The desired temperature after mixing at the exit of the chamber is $40^{\circ} \mathrm{C}$. There is no water leakage and the mixing happens at adiabatic conditions. Assume the specific heat capacity of water is $4.2 \mathrm{~kJ} / \mathrm{kg}-\mathrm{K}$. For a steady state operation, the mass flow rate (in $\mathrm{kg} / \mathrm{s}$) of the cold-water stream is
- $2.0$
- $1.5$
- $1.0$
- $0.5$
