Physics

Problem

A freezer door of area

0.50\,\text{m}^{2}

is constructed from three flat layers pressed firmly together: a

2.0\,\text{mm}

steel sheet (

k=45\,\text{W}/\text{m}\cdot\text{K}

), a

50\,\text{mm}

polyurethane foam core (

k=0.025\,\text{W}/\text{m}\cdot\text{K}

), and a

3.0\,\text{mm}

plastic interior panel (

k=0.20\,\text{W}/\text{m}\cdot\text{K}

). The room temperature is

25^{\circ}\text{C}

, and the freezer interior is maintained at

-10^{\circ}\text{C}

. Assuming steady conduction and negligible contact resistance, what is the best estimate of the thermal power conducted through the door? a) about

17\,\text{W}

b) about

0.9\,\text{W}

c) about

8.7\,\text{W}

d) about

26\,\text{W}