A 20 by 20 cm slab of copper 5 cm thick at a uniform temperature of 260◦C suddenly has its surface temperature lowered to 35◦C. Using the concepts of thermal resistance and capacitance and the...

A 20 by 20 cm slab of copper 5 cm thick at a uniform temperature of 260◦C suddenly
has its surface temperature lowered to 35◦C. Using the concepts of thermal
resistance and capacitance and the lumped-capacity analysis, find the time at which
the center temperature becomes 90◦C; ρ=8900 kg/m3, cp =0.38 kJ/kg · ◦C, and
k =370 W/m· ◦C.