Suppose that when we heat an aluminum rod, its length increases by 0.02%. What i

Question

Suppose that when we heat an aluminum rod, its length increases by 0.02%. What is the corresponding percent increase of the volume of the rod? A house is built of bricks, with walls 20 cm thick. The wall in one of the rooms of this house measures 5.0 m times 3.0 m. What is the heat flow through this wall if the inside temperature is 21 degree C and the outside temperature -18 degree C? Thermal conductivity k = 0.63 J/(s.m. degree C) The walls of houses built in Northeastern United States are commonly insulated with 6 in (15 cm) of fiberglass insulation. If you want to get the same insulation with hardwood walls, what should be the thickness of the wood? k_glass = 0.042 J/(s.m. degree C), k_wood = 0.13 J/(s.m. degree C) A piece of ice at 0 degree C is in contact with a piece of steel. If heat is flowing from the ice to the steel, what can you say about the temperature of the steel?

Explanation / Answer

10. Percentage increase in volume = 3 * percentage increase in length. = 3 * 0.02 = 0.06%

11. Amount of heat transferred per second, by conduction

= K*A*dT/dx = 0.63 * (21)-(-18) (5*3)/0.20 = 1842.8J/s

12. Q(wood) = Q(glass) => K(w)/x(w) = K(g)/x(g)

So thickness of wood x(w) = x(g)* K(w) /K(g)

X(w) =15(0.13)/(0.042) = 47.2cm

13. Ice melts at 0°c. Sono change in temperature occurs.

Hence the temperature of steel is 0°c.

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