A solid material has thermal conductivity K in kilowatts per meter-kelvin and temperature given at each point by w(x, y, z) = 15 - 4(x^2 + y^2 + z^2) °C. Use the fact that heat flow is given by the vector field F = -K∇w and the rate of heat flow across a surface S within the solid is given by -K ∬_S ∇w dS. Find the rate of heat flow out of a sphere of radius 1 (centered at the origin) inside a large cube of copper (K = 400 kW/(m · K)). (Use symbolic notation and fractions where needed.)
-K ∬_S ∇w dS = kW