100K,\] tem. Of surrounding \[{{T}_{0}}=0K\], initial temperature of body \[T=200\text{ }K\]]\[\frac{100}{dt}=\frac{\sigma 4\pi {{r}^{2}}}{\frac{4}{3}\pi {{r}^{3}}\rho CJ}({{200}^{4}}-{{0}^{4}})\]\[\RIGHTARROW dt=\frac{r\rho cJ}{48\sigma }\times {{10}^{-6}}s=\frac{r\rho c}{\sigma }.\frac{4.2}{48}\times {{10}^{-6}}\]\[=\frac{7}{80}\frac{r\rho c}{\sigma }\mu s\approx \frac{7}{72}\frac{r\rho c}{\sigma }\mu s[AsJ=4.2]\]