Question 6 A measure of 0.50 kg of water is placed in a 0.20 kg aluminium tray, both initially at 288 K, and placed in a refrigerator that is kept at 268 K. How long will it take to freeze the water and lower the temperature to 268 K if the maximum rate of removal of heat energy by the refrigerator is 50 W? Specific heat capacity of liquid water = 4.2 x 10 J kg K Specific heat capacity of ice = 2.1 x 10° J kg K Specific heat capacity of aluminium = 800 J kg K Latent heat of fusion of water = 3.4 x 10 J kg %3D

Question 6 A measure of 0.50 kg of water is placed in a 0.20 kg aluminium tray, both initially at 288 K, and placed in a refrigerator that is kept at 268 K. How long will it take to freeze the water and lower the temperature to 268 K if the maximum rate of removal of heat energy by the refrigerator is 50 W? Specific heat capacity of liquid water = 4.2 x 10 J kg K Specific heat capacity of ice = 2.1 x 10° J kg K Specific heat capacity of aluminium = 800 J kg K Latent heat of fusion of water = 3.4 x 10 J kg %3D

Physics for Scientists and Engineers: Foundations and Connections

1st Edition

ISBN:9781133939146

Author:Katz, Debora M.

Publisher:Katz, Debora M.

Chapter21: Heat And The First Law Of Thermodynamics

Section: Chapter Questions

Problem 68PQ

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(a) It is difficult to extinguish a fire on a crude oil tanker, because each liter of crude oil releases 2.80107J of energy when burned. To illustrate this difficulty, calculate the number of liters of water that must be expended to absorb the energy released by burning 1.00 L of crude oil, it the water has its temperature raised from 20.0C to 100C, it boils, and the resulting steam is raised to 300C. (b) Discuss additional complications caused by the fact that crude oil has a smaller density than water.
A person inhales and exhales 2.00 L of 37.0C air, evaporating 4.00102g of water from the lungs and breathing passages with each breath. (a) How much heat transfer occurs due to evaporation in each breath? (b) What is the rate of heat transfer in watts if the person is breathing at a moderate rate of 18.0 breaths per minute? (c) If the inhaled air had a temperature of 20.0C, what is the rate of heat transfer for warming the air? (d) Discuss the total rate of heat transfer as it relates to typical metabolic rates. Will this breathing be a major form of heat transfer for this person?
In cold climates, including the northern United States, a house can be built with very large windows facing south to take advantage of solar heating. Sunlight shining in during the daytime is absorbed by the floor, interior walls, and objects in the room, raising their temperature to 38.0C. If the house is well insulated, you may model it as losing energy by heat steadily at the rate 6 000 W on a day in April when the average exterior temperature is 4C and when the conventional heating system is not used at all. During the period between 5:00 p.m. and 7:00 a.m., the temperature of the house drops and a sufficiently large "thermal mass" is required to keep it from dropping too far. The thermal mass can be a large quantity of stone (with specific heat 850 J/kg C) in the floor and the interior walls exposed to sunlight. What mass of stone is required if the temperature is not to drop below 18.0C overnight?
(a) How much heat must be added to raise the temperature of 1.5 mol of air 25.0 to 33.0 at constant volume? Assume air is completely diatomic. (b) Repeat the problem for the same number of moles of xenon, Xe.
(a) Calculate the rate of heat transfer by radiation from a car radiator at 110C into a 50.0C environment, if the radiator has an emissivity of 0.750 and a 1.20m2 surface area. (b) Is this a significant fraction of the heat transfer by an automobile engine? To answer this, assume a horsepower of 200 hp (1.5 kW) and the efficiency of automobile engines as 25%.
(a) How much heat transfer is required to raise the temperature of a 0.750-kg aluminum pot containing 2.50 kg of water from 30.0 to the boiling point and then boil away 0.750 kg of water? (b) How long does this take if the rate of heat transfer is 500 W?
Unreasonable Results (a) What is the temperature increase of an 80.0 kg person who consumes 2500 kcal of food in one day with 95.0% of the energy transferred as heat to the body? (b) What is unreasonable about this result? (c) Which premise or assumption is responsible?
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 mailing 900 kg of ice? (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.
Two rods of the same length and diameter are made from different materials. The rods are to connect two regions of different temperature so that energy will transfer through the rods by heat. They can be connected in series, as in Figure 11.7a (page 363), or in parallel, as in Figure 11.7b. In which case is the rate of energy transfer by heat larger? (a) When the rods are in series. (b) When the rods are in parallel. (c) The rate is the same in both cases.
Equal masses of substance A at 10.0C and substance B at 90.0C are placed in a well-insulated container of negligible mass and allowed to come to equilibrium. If the equilibrium temperature is 75.0Q which substance has the larger specific heat? (a) substance A (b) substance B (c) The specific heats are identical. (d) The answer depends on the exact initial temperatures. (e) More information is required.
(a) 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 ale there in a 5.00-g peanut if the energy from burning it is transferred to 0. 500 kg of water held in a 0.100-kg aluminum cup, causing a 54.9- temperature increase? Assume the process takes place in an ideal calorimeter, in other words a perfectly insulated container. (b) Compare your answer to the following labeling information found on a package of dry roasted peanuts: a sewing of 33 g contains 200 calories. Comment on whether the values are consistent.
(a) A woman climbing the Washington Monument metabolizes 6.00102kJ of food energy. If her efficiency is 18.0%, how much heat transfer occurs to the environment to keep her temperature constant? (b) Discuss the amount of heat transfer found in (a). Is it consistent with the fact that you quickly warm up when exercising?