a
(a)
In steady state, rate of heat flow through both rods is equal.
$\operatorname{So},\left(\frac{k A\left(T_1-T\right)}{l}\right)_{\text {steel }}=\left(\frac{k A\left(T-T_2\right)}{l}\right)_{\text {copper }}$
Substituting given values, we have
$\frac{50 \times A (100- T ) t }{0.1}=\frac{400 \times( T -0) t }{0.2}$
$\Rightarrow 100(100-T) =400(T)$
$\Rightarrow T =20^{\circ} C$
