Radiation heat loss dominates for exposed faces

Steps:

• Identify primary heat loss mechanism: radiation, as convection/conduction minimized by insulation and identical setup.
• Recall Stefan-Boltzmann law: net radiation heat transfer proportional to surface area and emissivity (black > white).
• Compare areas: large face has greater area than small face, increasing total heat loss rate.
• Determine fastest cooling: maximum area and emissivity yield highest radiation rate.

Why A is correct:

• Large black face maximizes heat loss via high emissivity (near 1 for black) and large area, per Stefan-Boltzmann law (Q = εσA(T^4 - T_env^4)).

Why the others are wrong:

• B: White paint lowers emissivity (ε < 1), reducing radiation despite large area.
• C: Black paint aids emission, but small area limits total heat loss.
• D: White paint and small area both minimize radiation.

Final answer: A