You place a fireplace poker into the coals of a hot fire (500 degrees c). the poker is made of steel, 50cm long with a diameter of 1.5cm. a) if the other end of the rod is maintained at 31 degrees c, what heat current exists in the rod? b) how long does it take to transfer 10 kj of thermal energy? c) how would the answer to b change if the rod was copper?