A black body of mass $34.38\;g$ and surface area$19.2\;cm^2$ is at an initial temperature of $400\;K$. It is allowed to cool inside an evacuated enclosure kept at constant $0.04^{\circ}c$ per second. The specific heat of the body in $J\;kg^{-1} K^{-1}$ is : (Stefan's constant $\sigma = 5.73 \times 10^{-8} Wm ^{-2} K^{-4})$