An electric shower has a 1.5 kW heating element. (a).How much heat energy can it give out in five minutes? (b).If the element is used to heat 5 kg of water for 5 minutes, what would be the rise in temperature? (Specific heat capacity of water = 4180 J/kg).

In an air conditioner, 12.65 MJ of heat transfer occurs from a cold environment in 1.00 h. (a) What mass of ice melting would involve the same heat transfer?              (b) How many hours of operation would be equivalent to melting 900 kg ofice?                                                                                                                    (c) If ice costs 20 cents per kg, do you think the air conditioner could be operated more cheaply than by simply using ice? Describe in detail how you evaluate the relative costs.

The number of kilocalories in food is determined by calorimetry techniques in which the food is burned and the amount of heat transfer is measured. How many kilocalories per gram are there in a 9.56-g pistachio if the energy from burning it is transferred to 0.540 kg of water held in a 0.116-kg aluminum cup, causing a 57.7°C temperature increase? (You do not need to enter any units.) kcal/g Submit Answer Tries 0/10 Part B If a serving of pistachio consists of 16.0-g, how many kcal is consumed per serving? (Note: Food packaging energy content is labeled as "Cal" which is equivalent to "kcal".) (You do not need to enter any units.) kcal Submit Answer Tries 0/10

Problem 21. Newton's law of cooling states that the temperature of an object changes at a rate proportional to the difference between its temperature and that of its sur- roundings. Suppose that the temperature of a cup of coffee obeys Newton's law of cooling. The coffee has a temperature of 80°C when freshly poured, and 1 min later has cooled to 70°C, when the temperature outdoors is 0°C. (a) Write an initial value problem for this model. (b) Determine the time when the coffee reaches a temperature of 40°C. (Note: Begin the solution by stating your notation).