According to Stefan's law radiant energy emitted by a perfectly black body per unit area per sec ($ie,$ emissive power of black body) is directly proportional to the fourth power of its absolute temperature ie $E\propto T^4$

$\Rightarrow$ $\frac{E_1}{E_2}= \frac{T_1^4}{T_2^4}$

$\frac{5}{E_2}= \frac{{(273+227)}^4}{{(273+727)}^4}$

$E_2=5\times {\left[\frac{1000}{500}\right]}^4$

=$5\times 16=80 \mathrm{c}\mathrm{a}\mathrm{l}\mathrm{ }\mathrm{c}{\mathrm{m}}^{-2}{\mathrm{s}}^{-1}$