Heat is flowing through an annular wall of inside radius ro and temperature To and outside radius r1 with temperature T1. (see next page) The thermal conductivity k(T) varies linearly with temperature through this region, (a) Obtain an expression for the total heat flow through the wall evaluated at the outer surface.(b) Simplify the above result when (d is the annular thickness, much smaller than the inner radius) in which case and the geometry unravels

explanation:

an enlarged virtual image is the answer

what is the question because that is not a question.

it's when something is going so fast it makes a loud noise, breaking the sound barrier, for example: a jet makes a loud noise, not only cause of the jet but because they reached a point where they went so fast that you can year the noise from various parts, kinda like a police car, lets say the car was going   so fast that you hear the siren of the cop car right next to you, but the car is probably a mile a way, it's cos the siren was next to you a few seconds if you understand me