# Heat Problems

#### Superdreamer

I am unsure about some of my formulae and answers I would be very grateful if someone could clarify these please

Q1 The insulating layer on the inner wall of a building is made from a
compound layer of laminated board (inner) and styrofoam (outer). The
thickness of the board is 0.02 m and of the styrofoam, 0.06 m. If the
temperature at the surfaces of the layer are 20C (inner) and 5C (outer),
calculate the rate of flow of heat per m 2 through the layer and the
temperature at the board-styrofoam interface. The thermal conductivities
are 0.1 Js -1 m -1 C -1 for the board and 0.01 J s -1 m -1 C -1 for the styrofoam.

used the formula R=L/k to find the resistance of both then subbed in formula P=A(T2-T1)/(R1+R2)

Q2 Calculate the surface temperature of a human body of surface area 1.2
m 2 , which emits radiation at a rate of 597 W. Assume that the body
behaves as a perfect black body. If the temperature of the surroundings is
18° °° °C, calculate the net loss of heat by radiation by the body.

Used the formula Aε(5.6703x10^-8)T^4=Q/T=P

Orig temp T=291.16k
Aε(5.67...)(T2^4-T1^4)

Q3 Calculate the root mean square speed of nitrogen
molecules at 20 C. At what temperatures will the RMS speed be a) half that
value and b) twice that value?
The molar mass of nitrogen is 28x10 -3 kg mol -1 .

Vrms=sq root 3RT/M