WEBVTT 00:00:00.000 --> 00:00:03.240 This is College Physics Answers with Shaun Dychko. 00:00:03.560 --> 00:00:06.420 This question supposes that an 80.0 kilogram person 00:00:06.420 --> 00:00:09.780 consumes 2500 kilocalories of food energy 00:00:09.840 --> 00:00:14.260 and 95 percent of that energy is retained by the body as heat. 00:00:14.620 --> 00:00:17.020 So we convert the energy into joules 00:00:17.020 --> 00:00:20.460 by multiplying by 4186 joules per kilocalorie 00:00:20.520 --> 00:00:22.480 and we need to know the specific heat of the body 00:00:22.480 --> 00:00:25.740 which is 3500 joules per kilogram per Celsius degree. 00:00:26.300 --> 00:00:28.220 So the heat energy absorbed by the body then 00:00:28.220 --> 00:00:32.100 is going to be the total energy consumed multiplied by the efficiency 00:00:32.180 --> 00:00:34.980 by which it absorbs that heat energy— 00:00:35.180 --> 00:00:37.560 95 percent of it will be absorbed as heat— 00:00:37.660 --> 00:00:40.640 and that heat energy will also be the mass of the body 00:00:40.640 --> 00:00:42.980 times its specific heat times its change in temperature. 00:00:43.040 --> 00:00:44.800 So we can equate these two things 00:00:44.860 --> 00:00:48.600 and say that mcΔT equals energy times efficiency. 00:00:48.780 --> 00:00:52.580 Let's divide both sides by mc to solve for the change in temperature. 00:00:52.660 --> 00:00:54.940 So the change in temperature is energy times efficiency 00:00:54.940 --> 00:00:56.860 divided by mass times specific heat. 00:00:57.000 --> 00:01:02.420 So that's 1.0465 times 10 to the 7 joules times 0.95 divided by 80.0 kilograms 00:01:02.420 --> 00:01:05.140 times 3500 joules per kilogram per Celsius degree 00:01:05.280 --> 00:01:09.040 and that's a temperature change of 35.5 Celsius degree— 00:01:09.300 --> 00:01:11.260 that temperature change is huge. 00:01:11.360 --> 00:01:15.660 The body temperature is highly regulated around 37.0 degrees Celsius 00:01:15.720 --> 00:01:19.580 and a temperature change of more than 3.0 Celsius degrees is life-threatening. 00:01:19.620 --> 00:01:24.520 So a fever above 40.0 degrees Celsius needs medical assistance 00:01:24.520 --> 00:01:28.720 and this is 35 Celsius degrees above 00:01:28.780 --> 00:01:31.820 so highly impossible... totally impossible! 00:01:32.060 --> 00:01:33.720 And it's unreasonable to think 00:01:33.760 --> 00:01:36.100 that 95 percent of the heat generated from food 00:01:36.100 --> 00:01:38.480 will be retained by the body because the body has 00:01:38.480 --> 00:01:41.960 really good mechanism such as sweating to dissipate heat.