Need help with these physics problems

Question

a) Find the rate of energy flow through a copper block of cross-sectional area 15 cm2 and length 5.0 cm when a temperature difference of 20°C is established across the block.

_________J/s

(b) Repeat the calculation, assuming that the material is a block of stagnant air with the given dimensions.

__________J/s

(c) Repeat the calculation assuming, that the material is a block of wood with the given dimensions.

__________J/s

A box with a total surface area of 1.20 m2 and a wall thickness of 4.60 cm is made of an insulating material. A 10.0 W electric heater inside the box maintains the inside temperature at 16.5°C above the outside temperature. Find the thermal conductivity k of the insulating material.

__________W/m·K

Answer 1

For parts a, b, and c, use the formula

P = kA∆T / L

k is the thermal conductivity, A is the area (make sure you convert it into square meters), ∆T is the temperature difference, and L is the length

Here are the k values you need (I looked them up):

k (copper) = 397 W/m°C

k (air) = 0.0234 W/m°C

k (wood) = 0.08 W/m°C

All you have to do is plug in the values, which is incredibly easy, as long as you have a calculator.

For the last problem, use the formula I gave you earlier and solve for k.

k = PL / A∆T