If a rectangular block of rubber $($k $=0\mathrm{.}151$ W$/$m$$K$,$ Cp $=200$ J$/$kg$$K$,$ $=1201$ kg$/$m$3)$ is set out

in air at $297$ K to cool after being heated to a uniform temperature of $420$ K$,$ how long will it take

for the rubber surface to reach $320$ K$?$ The dimensions of the block are $0\mathrm{.}10$ m high by $1\mathrm{.}2$ m long

by $0\mathrm{.}55$ m wide. Assume most of the heat transfer happens on the top and bottom surfaces. The

heat transfer on the sides is negligible. The effective heat$$transfer coefficient at all exposed surface

is $6\mathrm{.}0$ W$/$m$2$K$.$

Answer: $0\mathrm{.}994$