Q$3$

A $4-mm$ diameter spherical ball at $50C$ is covered by a $1-$mm$-$thick plastic insulation with thermal conductivity, $k=0\mathrm{.}13\frac{W}{m}.K.$ The ball is exposed to a medium at $15C$ with a combined convection and radiation heat transfer coefficient of $20\frac{W}{m^2}K.$ Evaluate if the plastic insulation on the ball will help or hurt heat transfer from the ball.

$(4$ marks$)$