Physics

Problem

A concrete roof slab of area

100\,\text{m}^2

and thickness

15\,\text{cm}

is to be insulated with a layer of glass wool (thermal conductivity

0.04\,\text{W m}^{-1}\text{K}^{-1}

) so that the heat lost in

24\,\text{h}

does not exceed

1.5 \times 10^{8}\,\text{J}

when the inside temperature is

25^{\circ}\text{C}

and the outside temperature is

5^{\circ}\text{C}

. Neglecting the resistance of the concrete, determine the minimum thickness of glass wool required. a)

9.2\,\text{cm}

4.6\,\text{cm}

2.3\,\text{cm}

5.8\,\text{cm}