If in triangle ABC , with usual notations $\sin \frac{\mathrm{A}}{2} \cdot \sin \frac{\mathrm{C}}{2}=\sin \frac{\mathrm{B}}{2}$ and 2 s is the perimeter of the triangle, then the value of $s$ is

Two planets A and B have densities ' $\rho_1$ ', ' $\rho_2$ ' and have radii ' $r_1$ ', ' $r_2$ ', respectively. The ratio of acceleration due to gravity on $A$ to that of $B$ is

A rectangular black body of temperature $127^{\circ} \mathrm{C}$ has surface area $4 \mathrm{~cm} \times 2 \mathrm{~cm}$ and rate of radiation is E . If its temperature is increased by $400^{\circ} \mathrm{C}$ and surface area is reduced to half of the initial value then the rate of radiation is