✔ 最佳答案
(a) Mass of water circulated to the rooms = 1.5 x 1000 kg = 1500 kg
Amount of heat released = 1500 x 4200 x (80 - 60) J = 1.26 x 10^8 J
(b) Power = energy released/time
hence, time taken = 1.26x10^8/4.5x10^3 s = 28000 s = 7.78 hours
(c) The rate of heat released, in fact, depends on the difference in temperature of the water in the radiator and that inside the room (ambient temperatre). When the temperature of water in the radiator drops from 80'C to 60'C, the temperature difference gradually becomes smaller. Thus the rate of heat released drops.
2013-11-30 19:59:51 補充：
sorry...I have neglected the 15% heat loss. Thus,
(a) Heat released = 1.26 x 10^8 x (85/100) J = 1.071 x 10^8 J
(b) Time = 1.071x10^8/4.5x10^3 s = 23800 s = 6.61 hours
2013-12-03 11:09:48 補充：
126 MJ is the energy delivered by the water tank. But the question asks for the heat released to the room, which is 85% of 126 MJ.
