A $2\mathrm{.}11-$cm$-$diameter metallic sphere initially at $560C$ is being cooled by a $18C$ air stream. The heat transfer coefficient is $10\mathrm{.}1\frac{W}{m^2}-K.$ The specific

gravity of the metal is $7\mathrm{.}58$ and the specific heat of the metal is $0\mathrm{.}499k\frac{J}{k}g-K.$

Estimate the time necessary to cool the sphere to $36C.$

min