2.5 cm-thick sheet of plastic initially at 21°C is placed between two heated steel plates that
are maintained at 138°C. The plastic is to be heated just long enough for its midplane
temperature to reach 132°C. If the thermal conductivity of the plastic is 1.1 × 10-3 W/(m K),
the thermal diffusivity is 2.7 × 10-6 m2
/s, and the thermal resistance at the interface between
the plates and the plastic is negligible, calculate: (a) the required heating time, (b) the
temperature at a plane 0.6 cm from the steel plate at the moment the heating is discontinued,
and (c) t