AP EAMCET Engineering 21 Apr 2019 Shift 1 Paper

A solid copper sphere of density ρ. specific heat capacity C and radius r is initially at 200 K. It is suspended inside a chamber whose walls are at 0 K. The time required (in (is) for the temperature of the sphere to drop to 100 K is
(σ is Stefan's constant and all the quantities are in SI units)