Two concentric hollow spheres have radii 1 m and 2 m respectively. The space between them is filled with a material of thermal conductivity k. At time t=0, their temperatures are 273 K and 300 K respectively. Find the instantaneous heat current between the spheres.

Suppose a force of 60 n is required to stretch and hold a spring 0.1 m from its equilibrium position. a. assuming the spring obeys hooke's law, find the spring constant k. b. how much work is required to compress the spring 0.5 m from its equilibrium position? c. how much work is required to stretch the spring 0.6 m from its equilibrium position? d. how much additional work is required to stretch the spring 0.1 m if it has already been stretched 0.1 m from its equilibrium? a. kequals 600