 This was the first exam from the spring 2015 semester of Thermo one and it covered chapters one to two from the Moran and Shapiro Textbook that being said this was the semester when we were transitioning from the changlebook to the Moran and Shapiro book So this semester was a little bit of an overlap between the two Regardless though this exam had six multiple choice questions that made up 30% of the points and then five workout problems Which made up the other 70% of the points and we'll launch Directly into the multiple choice questions Question number one Specific volume is a specific property which means it is also an example of which type of property a Extensive be intensive see retail or D. None of the above Well, first of all we can eliminate retail Which simplifies the problem to is specific volume extensive intensive or neither? And I think that the easiest way to approach this problem is to think back to what a specific property is We defined a specific property as being an extensive property expressed per unit mass and A lot of people see that and they think well an extensive property per unit mass that must still be an extensive property, right? Well, when you take an extensive property Which is a property which changes based on how much of a substance you have and you divide it by mass Which is how much of a substance you have? The amount of mass kind of cancels and you end up with a property which doesn't change based on how much of it you have Which means that a specific property is also an intensive property So this was specific volume. It could have been any other specific property and it would have still been an intensive property Question number two Needing some extra caffeine on an early exam morning a student brings in a cup of 80 degrees Celsius coffee into a 23 degrees Celsius classroom After 30 minutes the coffee has reached 50 degrees Celsius and the temperature of the room has increased to 25 degrees Celsius At this moment the rate of heat loss from the coffee to the room should be Greater than when it started 30 minutes ago the same as when it started or less than when it started So let's consider what's actually happening here in Let's call the beginning of the process One state and the end of the process another state Shouldn't use A and B. I guess because this is multiple choice. Let's call it states one and two in a situation one at the beginning of the 30-minute cooling process we have coffee sitting in a room and the coffee is at 80 degrees Celsius and The room is at 23 degrees Celsius and at the end of the 30-minute period state two We assume that nothing else has happened in the room except for the cooling of the coffee and the heating of the air in the room so it is now 50 degrees Celsius coffee and A 25 degrees Celsius room So the question is how is the heat transfer between the coffee and the room in situation two Compared to the heat transfer from the coffee to the room in situation one is This less than this greater than this or the same as this So you might be a little bit hesitant to try to answer this question because you don't have enough information to actually calculate the rate of heat transfer from the Coffee to the room, but you don't need to actually calculate it All we need to know is that we defined heat transfer as being a function of the temperature difference between the two Substances which are exchanging heat So in this case it's going from the coffee to the air So what we care about is the change in temperature between the coffee and the air that temperature difference drives the heat transfer So in situation one we have a temperature difference of 80 minus 23 degrees Celsius Let me get out my calculator here. Okay, so 80 minus 23 degrees Celsius is a temperature difference of 57 degrees Celsius so in situation one the temperature difference of 57 degrees Celsius is driving the heat transfer in a situation two That would be 50 minus 25 which on most days is 25 So in situation two we have a temperature difference of 25 degrees Celsius driving the heat transfer between the coffee and the air So in situation two the temperature difference is lower. Therefore the heat transfer is lower So the rate of heat transfer is going to be less than when it started Question number three a student finds himself with little to do while vacationing in Daytona Beach over spring break Must be an engineering student to fill the time. He sets up an experiment He goes into a sealed room with no windows where the only source of light is four fluorescent light bulbs Which are 35 watts each he connects his pocket size solar panel Which he always carries to his laptop and lets the light from the bulbs charge his dead computer at one point during the Charging process his solar panel reads that he is supplying the laptop with 200 watts of power. Is this possible within the laws of thermodynamics? So this question is referring specifically to the first law of thermodynamics Whether or not energy can be created or destroyed So to answer this question we have to think about where the energy is coming from in this situation We have say a hypothetical room with 435 watt light bulbs and the question told us that There were no windows in this room So it's safe to assume that the only source of light are these 435 watt light bulbs So we could figure out the total amount of energy available in the light best case scenario would be whatever 4 times 35 is Let's see 2 would be 70 so 4 would be 140 But I was going to double-check so I know that the total amount of light energy Hypothetically available is 140 watts. So here If I'm getting 200 watts of power from the solar panels That solar panel would have to create energy in order to supply the laptop with 200 watts And because it's impossible to create or destroy energy We know that this process violates the first law of thermodynamics The only exception to this would be if the solar panel pack had Rechargeable batteries or something and the extra power was coming from that battery pack But that's outside the scope of this question Question number four The system diagram of the nozzle on the right is an example of which type of system a open system be closed system Or see isolated system So let's review what these mean in an open system both energy and mass are allowed to cross the boundary That's the boundary of the system in this case this nozzle This is sort of a side view of a nozzle the fluid is flowing through it in this direction We have a boundary set up for us already In a closed system energy is allowed to cross the boundary But mass isn't in an isolated system neither mass nor energy are allowed to cross the boundary So in this case we can see that the fluid flowing through the nozzle has to cross the boundary Therefore we have mass crossing the boundary the only system description which fits this type of scenario would be an open system This is best described as an open system Question number five a piston cylinder device filled with the gas is Expanded isothermally from a volume of 1.5 cubic meters to a volume of 2.5 cubic meters while keeping the mass of the gas constant If the system was selected as the mass of the gas inside the cylinder which type of system is this So again, we have the same three options available open system closed system or isolated system except in this case We aren't looking at a fluid passing through our system We have a gas inside a piston cylinder arrangement and over the course of the process. This is expanded But the system was selected as the mass of the gas inside the cylinder And it's safe to assume that no gas is escaping or entering around the piston head So it's reasonable to represent the system as one where the mass doesn't cross the boundary So we can immediately eliminate open system And the difference between a closed system and isolated system is whether or not energy crosses the boundary So to resolve this we have to think about what's happening and in this case It told us that the gas is expanding isothermally. So the temperature is constant throughout the process And now consider what's happening in expansion when you compress a gas It's going to try to heat up and the same is true for expansion when you expand a gas It tries to cool down So if this were a perfectly insulated system Then the temperature at the end of the process would probably be lower than at the start of the process So in order for the temperature to be the same it has to make up that energy with heat addition during the process So heat is a type of energy Therefore heat entering the system is a type of energy entering the system Therefore we should best represent this system as a closed system Question number six is this process explaining question five a steady or transient process well Remember that we defined a transient process as being one where properties change with time a steady process is one where properties Don't change in time So if you looked at a steady process Regardless of when you look at it all of the properties should be the same they might change with respect to Location you know if we were considering this nozzle up here if we Represented this as a steady process the temperature at the inlet of the nozzle could be different from the temperature at the outlet of the nozzle But for it to be steady both of these temperatures have to say constant with respect to time So if we consider this piston cylinder arrangement the mass is staying constant throughout the process the temperature staying constant but the volume is changing and That also means that the specific volume is changing because we have a different volume with the same amount of mass Therefore at least one property is changing with respect to time because presumably this process takes a non-zero amount of time to occur Therefore we have a transient process