Two circular discs A and ,B with equal radii are blackened. They are heated to same temperature and are cooled under identical conditions. What inference do your draw from their cooling curves?

When a body cools by radiation, the rate of cooling is given by:
                  $\frac{\mathrm{d\theta }}{\mathrm{dt}} = -\frac{\mathrm{eA\sigma }}{\mathrm{ms}}({\mathrm{\theta }}^4-{{\mathrm{\theta }}^4}_0)$
-ve sign shows that temperafure decreases, i.e., the body cools, s is the specific heat of material and ${\mathrm{\theta }}_0$ is the surrounding temperature
or $\frac{\mathrm{d\theta }}{\mathrm{dt}}\propto \frac{1}{\mathrm{s}}$
i.e., rate of cooling(R = $\frac{\mathrm{d\theta }}{\mathrm{dt}}$) is inversely proportional to the specific heat of material. For a, rate of cooling is large, therefore, specific heat of A is smaller.