PHYS 115 EXAM 1 Ch 15, 16, 17, 18 summer 2017
Equation for the submerged Volume (Vsub) of a solid of Volume (Vs) in fluid with density (pf)
Vsub = Vs (ps/pf) m^3
What is the equation for the buoyancy of a floating object?
W = pgV W = weight p = density of the object V= volume of the object
How much work is done in a constant volume process?
W=0 delta U = Q in constant volume processes
Will potatoes cook faster if the water is boiling faster?
Water boils at 100ºC and remains at that temperature until all of the water has been changed into steam. Only then will the steam increase in temperature. Because the water stays at the same temperature, regardless of how fast it is boiling, the potatoes will not cook any faster.
Adiabatic
When no heat flows in or out of a system, Q=0 Expansion: decrease in Pressure and Temperature Compression: increase in P & T Curve is similar to an isotherm, only steeper
You put 1 kg of ice at 0ºC together with 1 kg of water at 50ºC. What is the final temperature? • Lf = 80 cal/g • cwater = 1 cal/g ºC
0 ºC There is not enough heat to melt the ice
What are the two ways to change the buoyancy of an object?
1. Shape an object to displace more fluid than the volume of the object. 2. Alter the overall density. Example: using low-density heated air to fill hot-air balloons so they have an overall density less than air.
Water has a higher specific heat than sand. Therefore, on the beach at night, breezes would blow 1. from the ocean to the beach. 2. from the beach to the ocean. 3. either way, makes no difference.
2. from the beach to the ocean. Daytime: sun heats both the beach and the water beach heats up faster, warmer air above beach rises, cooler air from ocean moves in underneath, breeze blows ocean → land Nighttime: sun has gone to sleep, beach cools down faster, warmer air is now above the ocean cooler air from beach moves out to the ocean, breeze blows land → ocean.
A rectangular wooden block of weight W floats with exactly one-half of its volume below the waterline. Masses are stacked on top of the block until the top of the block is level with the waterline. This requires 20 g of mass. What is the mass of the wooden block?
20 g
Two objects are made of the same material, but have different masses and temperatures. If the objects are brought into thermal contact, which one will have the greater temperature change? 1. The one with the higher initial temperature 2. The one with the lower initial temperature 3. The one with the greater mass 4. The one with the smaller mass 5. The one with the higher specific heat
4. The one with the smaller mass Because the objects are made of the same material, the only difference between them is their mass. Clearly, the object with less mass will change temperature more easily because not much material is there (compared to the more massive object).
Which of the following statements are true? A) Solid ice is less dense than liquid water. B) Water contracts as it freezes at 0°C. C) Liquid water expands with increasing temperature above 4°C. D) Liquid water expands with increasing temperature between 0°C and 4°C.
A) True B) False C) True D) False
Which of the following conditions should be met to make a process perfectly reversible? a) Any mechanical interactions taking place in the process should be frictionless. b) Any thermal interactions taking place in the process should occur across infinitesimal temperature or pressure gradients. c) The system should not be close to equilibrium.
A, B
Which of the following statements are true for an isochoric (isovolumetric) process? Check all that apply. a) During an isochoric process, the work done by the gas on its surroundings is zero. b) During an isochoric process, the internal energy of the system changes. c) An isochoric process is carried out at constant volume. d) An isochoric process is carried out at constant pressure. e) An isochoric process is carried out at constant temperature.
A, B, C are true
Which of the following statements are true for an isothermal process? a) During an isothermal process, the work done by the gas equals the heat added to the gas b) An isothermal process is carried out at constant pressure. c) An isothermal process is carried out at constant temperature. d) An isothermal process is carried out at constant volume. e) During an isothermal process, the internal energy of the system changes.
A, C
Which of the following statements are true? Check all that apply. a) The first law of thermodynamics extends the principle of conservation of energy to include heat as well as mechanical energy. b) The amount of heat added or removed from a thermodynamic system depends only on the initial and final states of the system. c) The amount of heat added or removed from a thermodynamic system depends on the path taken on a pV diagram. d) The work done by a thermodynamic system is equal to the area under the curve on a pV diagram. e) The work done by a thermodynamic system depends only on the initial and final states of the system. f) The first law of thermodynamics extends the principle of conservation of momentum to include molecular collisions.
A, C, D
Which of the following statements are true for an isobaric process? a) An isobaric process is carried out at constant pressure. b) An isobaric process is carried out at constant volume. c) During an isobaric process, the work done by the gas equals the heat added to the gas. d) An isobaric process is carried out at constant temperature. e) During an isobaric process, the internal energy of the system changes.
A, E
Consider water outside a closed container (e.g. sweat on your skin). Which of the following is true of such an 'open' liquid? A.It will not reach equilibrium with its vapor and will keep vaporizing without reaching equilibrium. B.It will reach equilibrium with its vapor and that is why it vaporizes
A.It will not reach equilibrium with its vapor and will keep vaporizing without reaching equilibrium. The molecules that escape are the higher-energy ones, this has a cooling effect on the liquid
Given your experience of what feels colder when you walk on it, which of the following surfaces would have the highest thermal conductivity? 1. rug 2. steel surface 3. concrete floor 4. Has nothing to do with thermal conductivity
Answer: 2) steel The heat flow rate is k A (T1 − T2)/l. All things being equal, bigger k leads to bigger heat loss. From the book: Steel = 40, Concrete = 1.3, Human tissue = 0.2, Wool = 0.04, in units of W/(m-K)
second law of thermodynamics in regards to entropy
Any process occurring in a closed system either increases the entropy (disorder) of the system or leaves it constant. For irreversible processes, the entropy increases; for the reversible ones, the entropy remains constant.
Based on the results found in the previous question, which of the following processes are not reversible? a) Melting of ice in an insulated ice-water mixture at 0∘C. b) Lowering a frictionless piston in a cylinder by placing a bag of sand on top of the piston. c) Lifting the piston described in the previous statement by removing one grain of sand at a time. d) Freezing water originally at 5∘C.
B, D
When bricks A & B are placed in thermal contact, energy flows from brick B to Brick A. Which brick had the higher internal temperature?
Brick B
Which of the following statements are true for an adiabatic process? a) An adiabatic process is carried out at constant pressure. b) An adiabatic process is carried out at constant temperature. c) During an adiabatic process, the internal energy of the system changes. d) An adiabatic process is carried out at constant volume. e) During an adiabatic process, there is no heat transfer into or out of the system.
C, E
What is the primary mode of energy transfer from your bare feet to a cold ceramic bathroom floor in the middle of winter?
Conduction
What is the primary mode of the flow of energy from your tongue to a metal railing if you happen to lick it on a cold winter day?
Conduction
What is the primary mode of energy transfer away from your body on a very windy day?
Convection
What is the primary mode of energy transfer from your body to your hands when you blow on them to warm them?
Convection
How does the molar specific heat at constant pressure (Cp) compare with the molar specific heat at constant volume (Cv)?
Cp > Cv When heat is added to Cv, the heat goes entirely toward increasing the temperature, no work is done. When heat is added to Cp, the temp is increased AND work is done, so it takes more heat to raise the temp the same amount.d
Two identical cylinders at the same temperature contain the same gas. If cylinder A contains three times as much gas as cylinder B, which cylinder has the higher pressure?
Cylinder A has the higher pressure For constant V and T, the one with more gas (the larger value of n) has the higher pressure P.
How can entropy behave in an isolated/closed system?
Entropy can increase as it approaches equilibrium or stay constant in a closed system. It CAN NOT decrease spontaneously.
Is the entropy of a bag of popcorn greater than, less than, or equal to the entropy of the kernels of corn before popping?
Entropy of the popped corn is greater because popping the corn is an irreversible process.
T/F The thermodynamic processes that occur in nature are reversible.
False Only infinitely slow, or quasi-equilibrium, processes can be reversible; such processes exist only in the imaginations of scientists.
A rectangular wooden block of weight W floats with exactly one-half of its volume below the waterline. What is the buoyant force acting on the block?
Fb = Weight of the block
What is the equation for a buoyancy?
Fb = pgV p = density of the fluid V= volume of the object
If an object is less dense than the material it is immersed in, how will its Fb when completely immersed relate to its Weight?
Fb > weight
How can a metal that is denser than water float?
If metal is shaped to displace more water than the volume of the metal itself then it can float. Example: metal in the shape of a bowl instead of a block.
As you found out in the previous part, Bernoulli's equation tells us that a fluid element that flows through a flow tube with decreasing cross section moves toward a region of lower pressure. Physically, the pressure drop experienced by the fluid element between points 1 and 2 acts on the fluid element as a net force that causes the fluid to __________.
Increase in speed
you put a tray of water in the kitchen freezer and some time later it has turned to ice. Has the entropy of the universe increased, decrease, or stayed the same?
Increased Although heat is removed from water to freeze it and removing heat from an object lowers its entropy - the freezer does work to draw heat from the water and exhausts more heat into the kitchen than it absorbs from the water. Entropy increase of heated air in kitchen is greater than the entropy decrease of the water.
Isochoric
Isovolumetric
What happens to the entropy of a bucket of water as it is cooled down (but not frozen)? It increases. It decreases. It stays the same.
It decreases. Qh is negative, energy is given to surroundings. Presumably, the bucket is not isolated: Heat must be transferred to another object, which is most likely at a lower temperature than that of the bucket.
What happens to the entropy of a cube of ice as it is melted? It increases. It decreases. It stays the same.
It increases. (Qh is positive)
What happens to the entropy of a piece of wood as it is burned? It increases. It decreases. It stays the same.
It increases. When a solid object is turned into a gas, the degree of disorder increases, so the entropy increases.
When water boils at the top of a mountain, is its temperature greater than, less than, or equal to 100 degrees C?
Less than Patm at the top of a mountain is less than sea level so the BP is lower
Two metal rods are to be used to conduct heat from a region at 100 C to a region at 0 C. The rods can be placed in parallel or in a series (end to end). a) is the heat conducted in the parallel arrangement greater than, less than, or the same as the heat conducted with the rods end to end? Why?
More heat is conducted when the rods are parallel. The cross-sectional area through which heat flows is greater when the rods are parallel.
which requires more heat: melting 100 kg of copper or boiling 10 kg of water? Lf Cu = 20.7 x 10^4 Lv H2O = 22.6 x 10^5
More heat is required to boil water Q = m(Lf or Lv) Q = 100 kg (20.7 x 10^4) = 2.07 x 10^7 Q = 10 kg (22.6 x 10^5) = 2.26 x 10^7
Consider the portion of a flow tube shown in the figure. (Figure 1) Point 1 and point 2 are at the same height. An ideal fluid enters the flow tube at point 1 and moves steadily toward point 2. If the cross section of the flow tube at point 1 is greater than that at point 2, what can you say about the pressure at point 2?
P2 < P1 By combining the continuity equation and Bernoulli's equation, one can characterize the flow of an ideal fluid.When the cross section of the flow tube decreases, the flow speed increases, and therefore the pressure decreases. In other words, if A2<A1, then v2>v1 and p2<p1.
You step out of a swimming pool on a hot day, where the air temperature is 90ºF. Where will you feel cooler, in Phoenix (dry) or in Philadelphia (humid)?
Phoenix (dry) In Phoenix, where the air is dry, more of the water will evaporate from your skin. This is a phase change, where the water must absorb the heat of vaporization, which it takes from your skin. That is why you feel cool as the water evaporates.
Due to the evaporation of the jogger's sweat, the change in entropy of the universe is: Not able to be determined with the given information Negative Positive Zero
Positive The change in entropy of the jogger is negative, so the universe must have a positive change in entropy.
In a closed system, is delta S positive or negative as heat is transferred from a hotter object to a colder one?
Positive, entropy (disorder) increases.
Q (+ or -) system GAINS heat Q (+ or -) system LOSES heat W (+ or -) work done BY system W (+ or -) work done ON system
Q + system GAINS heat Q - system LOSES heat W + work done BY system W - work done ON system
When is Qh negative? Positive?
Qh is negative when thermal energy is given to surroundings. Qh is positive when thermal energy is absorbed from surroundings.
What is the primary mode of energy transfer from your body on a cold day with no wind?
Radiation
What is the primary mode of energy transfer from hot coffee inside a Thermos bottle to the environment
Radiation The thermos creates a vacuum, no energy is exchanged with the environment.
If the Sun's surface temperature falls to half the current surface temperature, by what factor will the radiant energy reaching the Earth change?
Radiation energy is proportional to T4. So if temperature is halved, radiation energy will decrease by a factor of 16.
Why does adding salt to water raise the BP?
Salt dissolves into Na+ and Cl- which have strong interactions with the water molecules, making it harder for them to break free and enter vapor phase. This causes a higher BP, this is helpful in solidifying any material that might leak out of boiling eggs, for example.
Is the "size" of a degree in the Fahrenheit scale greater than, less than, or equal to the size of a degree on the Kelvin scale?
Smaller. F degrees are "smaller" than Kelvin degrees because there are 180 F degrees b/freezing and boiling water, but only 100 Kelvin degrees.
Water flows through a horizontal pipe. The diameter of the pipe at point B is larger than the diameter of the pipe at point A. Where is the speed of the water the greatest?
Speed of water is greatest at point A. A1v1 = A2v2 A = area v = velocity
Which is worse: a steam burn or a water burn both at 100 C?
Steam burn is more severe Water will cool to skin temp right away; steam has to give off heat to condense to water, then will cool. Heat transferred to skin from steam is much higher than water.
System 1 is at 0 C and System 2 is at 0 F. If these systems are placed in thermal contact, which way will the heat flow? (18)
System 1 -> System 2 1) 0 C = 32 F 2) 0 F = -18 C
In system A, the heat Q is added to a cold reservoir with a temperature of 300 K. In system B, the same heat is added to a cold reservoir with a temperature of 350 K. Is the increase in entropy for system A greater than, less than, or equal to the increase in entropy for system B?
System A has greater increase in entropy than system B delta S = Q/T
What is the one thing the internal energy of an ideal gas depends on?
Temperature U=3/2 nRT
If both the pressure and volume of a given sample of an ideal gas are doubled, what happens to the temperature of the gas in Kelvins?
Temperature quadruples
Th, Tc
Th: the absolute temperature of the outside; and Tc: the absolute temperature of the inside.
Feeling a bit cool, you turn up the thermostat in your living room. A short time later the air is warmer. Assuming the room is well sealed, is the pressure of the air greater than, less than, or the same as before you turned up the heat?
The air pressure is greater. Since the room is sealed, the # of molecules and their volume is constant. PV = NkT, increase in T means an increase in P
On the side of a cargo ship you see two maximum load lines, one for saltwater and one for freshwater. Which line is the one for saltwater, the top or the bottom line?
The bottom line. Salt water is denser than freshwater, less of it needs to be displaced to provide a given buoyancy force. A ship floats higher in saltwater.
Is the buoyant force exerted on a cubical block of aluminum 10 cm on a side greater than, less than, or equal to the Fb exerted on a cubical block of lead 10 cm on a side when both are completely submerged in water?
The buoyant forces are equal because they displace the same amount of water.
Suppose the glass in a glass thermometer expands more with temperature than the mercury it holds.
The mercury level would drop with increasing temperature.
Each of two containers of equal volume hold an ideal gas. container A has twice as many molecules as container B. I the gas pressure is the same in the two containers, is the rms speed of the molecules in container A greater than, less than, or the same as the rms speed of the molecules in container B?
The rms speed is less in container A. remember that the pressure of a gas is caused by the collisions of gas molecules with the walls of the container. If more molecules occupy a given volume and they bounce off the walls with the same speed as in a container with few molecules, the pressure will be greater. So for the pressure to be the same, the rms speed of the molecules in container A have to be less than the rms speed in container B.
An engineer proposes an engine that essentially takes heat from the cooler ocean and powers a submarine, then expels heat to the atmosphere. Does this violate the first law of thermodynamics, the second law, or both? The first law The second law Both
The second law This does not violate the first law of thermodynamics depending on the values of Q, but it does violate the second law of thermodynamics, as heat is flowing from the cold sea to the warmer atmosphere.
What is the slope of the fusion line of water and what does that mean?
The slope is negative. This is because ice is less dense than water. If temp is held constant and pressure is applied to ice, the ice will melt. This is how glaciers move, the high pressure melts the bottom layer of ice, creating a low-friction layer that the top layer slides on. This is also how ice skates work.
What is the slope of the fusion line of most substances and what does that mean?
The slope is usually positive. As pressure increases, the melting temp of a substance also increases. Applying pressure to a liquid (with constant temp) will make the liquid more dense and eventually solidify.
The pressure of a system doubles during an isothermal process. What happens to its volume?
The volume is halved because P and V are inversely related in isothermal processes.
Your friend claims that stirring a glass of water with a spoon increases the temperature of the water. Is she correct?
Yes, part of the mechanical work done in stirring the water goes into increasing its temperature.
What is the entropy for a full cycle?
Zero. After a complete cycle the system returns to its original state so the change in entropy is 0.
Why must every heat engine have a cold reservoir? a) Because it is impossible for even a perfect engine to convert heat entirely into mechanical work. b) Because the cold reservoir keeps the engine from overheating. c) Because the cold reservoir keeps the engine from overcooling. d) Because the cold reservoir increases the power of the engine.
a) Because it is impossible for even a perfect engine to convert heat entirely into mechanical work.
The specific heat capacity of aluminum is about twice that of iron. Consider two blocks of equal mass, one made of aluminum and the other one made of iron, initially in thermal equilibrium. Heat is added to each block at the same constant rate until it reaches a temperature of 500 K. Which of the following statements is true? a) The iron takes less time than the aluminum to reach the final temperature. b) The aluminum takes less time than the iron to reach the final temperature. c) The two blocks take the same amount of time to reach the final temperature.
a) The iron takes less time than the aluminum to reach the final temperature.
An ice cube is placed in a cup of water. A few minutes later half the ice has melted, and the remainder is in equilibrium with the water. a) was the Ti >, <, = 0 deg C? b) is the Tf >, <, = 0 deg C?
a) Ti > 0 because some of the ice melts b) Tf = 0 because there is still some ice, the system is in equilibrium
Two identical springs are connected end to end. a) is the force constant of the resulting compound spring greater than, less than, or equal to the force constant of a single spring? b) which of the following is the best explanation for the prediction? i. the resulting force constant is greater because two springs are acting together, doubling the force. ii. the two springs produce a longer compound spring - but the material is the same, and therefore the force constant is the same as well. iii. the force constant is less for the compound spring because it stretches twice as far for the same applied force.
a) force is less by factor of 2 F = Y (delta L/Li) A = kx b) iii. the force constant is less for the compound spring because it stretches twice as far for the same applied force.
A partially filled flask of water rests on a scale. a) if you dip your finger in the water without touching the flask, does the reading on the scale increase, decrease, or stay the same? B) what is the best explanation for this?
a) the reading on the scale increases b) The upward Fb on the finger results in a downward force on the flask, which increases the reading on the scale
you haven't had time to install your new air conditioner in the window yet, so as a short-term measure you decide to place it on the dining-room table and turn it on to cools things off. a) does the air in the dining room get warmer, cooler, or stay the same temp? b) why?
a) the room gets warmer b) the room gets warmer due to the combined effect of the heat exhausted by the a/c and the work done by its motor.
How would you increase the coefficient of performance of an ideal refrigerator? a) Increase the mechanical work input. b) Decrease the outside temperature. c) Decrease the inside temperature. d) Increase the outside temperature.
b) Decrease the outside temperature. The efficiency e of an ideal/Carnot refrigerator that absorbs heat Qc from a reservoir at a temperature Tc, and releases heat Qh to another reservoir at a temperature Th, with a work input |Win|=|Qc|−|Qh|, is e=Qc|Win|=TcTh−Tc. From this equation, you can see that decreasing Th and/or increasing Tc lead to an increase in the efficiency e.
A cube of wood is floating on water. A cube of iron is totally submerged in water. The cubes are equal in volume. Which cube has the greater buoyant force acting on it? a) The buoyant force cannot be determined without additional information. b) The cube of iron has the greater buoyant force acting on it. c) Both cubes have the same buoyant force acting on it. d) The cube of wood has the greater buoyant force acting on it.
b) The cube of iron has the greater buoyant force acting on it. The cube of iron is displacing more water
A piece of wood is floating in a tub of water. A second piece of wood rest on top of the first piece; it does NOT touch the water. If the second piece is removed from the first and placed in the water, what happens to the water level in the tub? a) The water level cannot be determined without additional information. b) The water level remains unchanged. c) The water level drops. d) The water level rises.
b) The water level remains unchanged.
The pressure at 10 m below the surface of the ocean is about 2.00×10^5 Pa Which of the following is true? a) The weight of a column of seawater 1 m2 in cross section and 10 m high is about 2.00×10^5 N. b) The weight of a column of seawater 1 m2 in cross section and 10 m high plus the weight of a column of air with the same cross section extending up to the top of the atmosphere is about 2.00×10^5 N. c)The weight of 1 m3 of seawater at 10 m below the surface of the ocean is about 2.00×10^5 N. d)The density of seawater is about 2.00×10^5 times the density of air at sea level.
b) The weight of a column of seawater 1 m2 in cross section and 10 m high plus the weight of a column of air with the same cross section extending up to the top of the atmosphere is about 2.00×10^5 N.
A cup is filled to the brim with water and a floating ice cube. Resting on top of the ice cube is a small pebble. When the ice melts, which of the following occurs: a) water overflows the cup b) the water level is lower c) the water level remains the same
b) the water level is lower The ice makes no difference to the water level. The pebble displaces a volume of water equal to its weight when on top of the ice. When the pebble drops to the bottom of the cup, it displaces a volume of water equal to its own volume. volume of the pebble is less than the volume of water with the same weight --> water level is lower.
A flat metal washer is heated. As the washer's temperature increases, what happens to the hole in the center? a) Changes in the hole cannot be determined without know the composition of the metal. b)The hole in the center of the washer will expand. c)The hole in the center will remain the same size. d)The hole in the center of the washer will contract.
b)The hole in the center of the washer will expand. Everything expands when heated
If the Kelvin temperature of a gas is doubled, by what factor does the root mean square speed of the molecules increase?
by the square root of 2
What is the relationship between area, force, and pressure? a) Pressure is proportional to both force and area. b) Pressure is inversely proportional to force and proportional to area. c) Pressure is proportional to force and inversely proportional to area. d) Pressure is inversely proportional to both force and area.
c) Pressure is proportional to Force and inversely proportional to Area P = F/A
The specific heat capacity of aluminum is about twice that of iron. Consider two blocks of equal mass, one made of aluminum and the other one made of iron, initially in thermal equilibrium. When the two materials have reached thermal equilibrium, the block of aluminum is cut in half and equal quantities of heat are added to the iron block and to each portion of the aluminum block. Which of the following statements is true? a) The three blocks are no longer in thermal equilibrium; the iron block is warmer. b) The three blocks are no longer in thermal equilibrium; both the aluminum blocks are warmer. c) The blocks remain in thermal equilibrium.
c) The blocks remain in thermal equilibrium. Since the same quantities of heat are added to samples that have different masses and different specific heat capacities, this may result in different final temperatures for each sample. However, you must keep in mind that each smaller block of aluminum now has half the mass of the iron block, but about twice the specific heat capacity. To solve this problem use proportional reasoning to find a relation between ΔT, c, and m.
If the coefficient of performance of a refrigerator is 1, which the following statements is true? a) The temperature outside equals the temperature inside of the refrigerator. b) The rate at which heat is removed from the inside equals the rate at which heat is delivered outside. c) The power consumed by the refrigerator equals the rate at which heat is removed from the inside. d) The power consumed by the refrigerator equals the rate at which heat is delivered to the outside.
c) The power consumed by the refrigerator equals the rate at which heat is removed from the inside. COP = Qc / W
Now consider the pressure 20 m below the surface of the ocean. Which of the following statements is true? a) The pressure is twice that at a depth of 10 m. b) The pressure is the same as that at a depth of 10 m. c) The pressure is equal to that at a depth of 10 m plus the weight per 1 m2 cross sectional area of a column of seawater 10 m high. d) The pressure is equal to the weight per 1 m2 cross sectional area of a column of seawater 20 m high.
c) The pressure is equal to that at a depth of 10 m plus the weight per 1 m2 cross sectional area of a column of seawater 10 m high.
According to the second law of thermodynamics, it is impossible for ____________. a) heat energy to flow from a colder body to a hotter body b) an ideal heat engine to have the efficiency of 99% c) an ideal heat engine to have non-zero power. d) a physical process to yield more energy than what is put in
c) an ideal heat engine to have non-zero power. The ideal engine follows a reversible cycle--therefore, an infinitely slow one. If the work is being done at the infinitely slow rate, the power of such an engine is zero.
To increase the efficiency of an ideal heat engine, one must increase which of the following? a) the amount of heat consumed per second b) the temperature of the cold reservoir c) the temperature of the hot reservoir d) the size of the cold reservoir e) the size of the hot reservoir
c) the temperature of the hot reservoir e(max) = 1 - Tc/Th
a cup is filled to the brim with water. Floating on the water is an ice cube, on top of which rests a small block of wood. When the ice melts, and the block of wood floats in the water, the following occurs: a) water overflows the cup b) the water level is lower c) the water level remains the same
c) the water level remains the same The wood displaces the same amount of water whether it rests on the ice cube or floats by itself.
A cup is filled to the brim with water and a floating ice cube. When the ice melts, which of the following occurs: a) water overflows the cup b) the water level is lower c) the water level remains the same
c) the water level remains the same when the ice cube melts the weight is the same, the melted water fills the same volume the ice cube displaces.
Second law of thermodynamics
heat always flows from a hot object to a cool object, never in reverse
How can entropy behave in an open system?
it can increase, decrease, or stay the same
What is the primary mode of energy transfer into your sealed car parked in the sun on a hot summer day?
radiation
Objects A & B have the same mass. When they receive the same amount of thermal energy, the temperature of object A increases more than the temp of object B. Is the specific heat of object A greater than, less than, or equal to the specific heat of object B?
specific heat of A < specific heat of B Temp increase is inversely proportional to specific heat.
Qc:
the (positive) amount of heat absorbed from the "inside" during one cycle or during some time specified in the problem;
Qh:
the (positive) amount of heat delivered to the "outside" during one cycle or during some time specified in the problem;
W:
the amount of external work input during one cycle or during some time specified in the problem;
Which feels coolers, walking on tile or carpet? Why?
tile feels cooler Tile has a larger thermal conductivity than carpet so more heat flows from your skin to the tile than the carpet.
A vehicle has a soft, ragtop roof. When the car is at rest, the roof is flat. When the car is cruising at highway speeds with its windows rolled up, does the roof bow upward, remain flat, or bow downward?
upward since the windows are closed the air inside is at rest, the air flowing over the top is in motion and has less pressure, causing the roof to bow upward
If you add some heat to a substance, is it possible for the temperature of the substance to remain unchanged?
yes Yes, it is indeed possible for the temperature to stay the same. This is precisely what occurs during a phase change—the added heat goes into changing the state of the substance (from solid to liquid or from liquid to gas) and does not go into changing the temperature
