A spherical object of $9-cm$ in diameter is initially at a uniform temperature of $20C.$

Suddenly it is subjected to freezing air cooling at $-15C$ with a heat transfer coefficient of $10$

$\frac{W}{m^2}*K.$ Determine the temperatures at the center and surface and the heat loss after $3807$

seconds. Properties of this object: $=840k\frac{g}{m^3},c_p=3\mathrm{.}81k\frac{J}{k}g*K,k=0\mathrm{.}45\frac{W}{m}*K,$ and $=$

$1\mathrm{.}4{10}^{-7}\frac{m^2}{s}.$