Thermodynamics

1.2 in.Furnace, 1300°FBrassplate, 75°FFIGURE P4–83E4–84 Long cylindrical steel rods (r 7833 kg/m 3 and c p 0.465 kJ/kg · °C) of 10-cm diameter are heat-treated by drawingthem at a velocity of 3 m/min through an oven maintainedat 900°C. If the rods enter the oven at 30°C and leaveat a mean temperature of 700°C, determine the rate of heattransfer to the rods in the oven.Special Topic: Biological Systems4–85C What is metabolism? What is basal metabolic rate?What is the value of basal metabolic rate for an average man?4–86C For what is the energy released during metabolismin humans used?4–87C Is the metabolizable energy content of a food thesame as the energy released when it is burned in a bombcalorimeter? If not, how does it differ?4–88C Is the number of prospective occupants an importantconsideration in the design of heating and cooling systemsof classrooms? Explain.4–89C What do you think of a diet program that allows forgenerous amounts of bread and rice provided that no butter ormargarine is added?4–90 Consider two identical rooms, one with a 2-kW electricresistance heater and the other with three couples fastdancing. In which room will the air temperature rise faster?4–91 Consider two identical 80-kg men who are eatingidentical meals and doing identical things except that one ofthem jogs for 30 min every day while the other watches TV.Determine the weight difference between the two in amonth. Answer: 1.045 kg4–92 Consider a classroom that is losing heat to the outdoorsat a rate of 20,000 kJ/h. If there are 30 students inclass, each dissipating sensible heat at a rate of 100 W, determineif it is necessary to turn the heater in the classroom onto prevent the room temperature from dropping.4–93 A 68-kg woman is planning to bicycle for an hour.If she is to meet her entire energy needs while bicycling byeating 30-g chocolate candy bars, determine how many candybars she needs to take with her.Chapter 4 | 2094–94 A 55-kg man gives in to temptation and eats an entire1-L box of ice cream. How long does this man need to jogto burn off the calories he consumed from the ice cream?Answer: 2.52 h4–95 Consider a man who has 20 kg of body fat when hegoes on a hunger strike. Determine how long he can surviveon his body fat alone.4–96 Consider two identical 50-kg women, Candy andWendy, who are doing identical things and eating identicalfood except that Candy eats her baked potato with four teaspoonsof butter while Wendy eats hers plain every evening.Determine the difference in the weights of Candy and Wendyafter one year. Answer: 6.5 kg4–97 A woman who used to drink about one liter of regularcola every day switches to diet cola (zero calorie) and startseating two slices of apple pie every day. Is she now consumingfewer or more calories?4–98 A 60-kg man used to have an apple every day afterdinner without losing or gaining any weight. He now eats a200-ml serving of ice cream instead of an apple and walks 20min every day. On this new diet, how much weight will helose or gain per month? Answer: 0.087-kg gain4–99 The average specific heat of the human body is3.6 kJ/kg · °C. If the body temperature of an 80-kg man risesfrom 37°C to 39°C during strenuous exercise, determine theincrease in the thermal energy of the body as a result of thisrise in body temperature.4–100E Alcohol provides 7 Calories per gram, but it providesno essential nutrients. A 1.5 ounce serving of 80-proofliquor contains 100 Calories in alcohol alone. Sweet winesand beer provide additional calories since they also containcarbohydrates. About 75 percent of American adults drinksome sort of alcoholic beverage, which adds an average of210 Calories a day to their diet. Determine how many poundsless an average American adult will weigh per year if he orshe quit drinking alcoholic beverages and started drinking dietsoda.4–101 A 12-oz serving of a regular beer contains 13 g ofalcohol and 13 g of carbohydrates, and thus 150 Calories. A12-oz serving of a light beer contains 11 g of alcohol and 5 gRegularbeer12 oz.150 calLightbeer12 oz.100 calFIGURE P4–101