Unsteady State 1D Heat Conduction in Cartesian Coordinate System without Heat Generation

Q. Temperature distribution at certain instant of time across a wall of thickness 1 m is given by $T=800-300x-50x^2$. The wall has a constant heat generation of $1000{\text{W/m}}^3$. Density of material is $1600{\text{kg/m}}^3$, thermal conductivity is 40 W/mK and specific heat of material is 3 kJ/kgK. What will be the rate of change of internal energy of wall for per unit cross-sectional area ?

1. 5 kJ/s, increasing
2. Can't be determined from given data
3. 3 kJ/s, decreasing
4. 3 kJ/s, increasing