Heat radiations propagate with the speed of

Heat energy is incident on the surface of a material at the rate of $1000 \ J \ min^{-1}$. If the coefficient of absorption is $0.8$ and the coefficient of reflection is $0.1$,then the amount of heat energy transmitted through the material in $5$ minutes is: (in $J$)

$A$ hot and a cold body are kept in vacuum separated from each other. Which of the following causes a decrease in the temperature of the hot body?

The surface of a thermos flask is kept shiny because:

$A$ sphere,a cube,and a thin circular plate,all made of the same material and having the same mass,are initially heated to a temperature of $1000^{\circ}C$. Which one of these will cool first?

Which of the following statements is true for a perfectly black body?