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ATTN: PHYSICS FOLKS! Help Me!
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The specific heat capacity of iron is approximately half that of
aluminum. Two balls of equal mass, one made of iron and the other
of aluminum, both at 80 °C, are dropped into a thermally insulated
jar that contains an equal mass of water at 20 °C. Thermal
equilibrium is eventually reached. Which one of the following
statements concerning the final temperatures is true?
A. Both balls will reach the same final temperature.
B. Iron ball will reach higher final temp than aluminum ball.
C. Aluminum ball will reach higher final temp than iron ball.
D. Diff in final ball temps depends on initial mass of water.
E. Diff in final ball temps depends on initial temp of water.
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I believe its a) that they reach the same temp.
The specific heat doesnt really come into play here if your not measuring stuff such as the increase of the water temp etc...Im not even sure they give you enough info if you wanted to try and do it that way.
note key words though:
"thermal equilibrium"
(ie, shits at the same temp)
The heat transfer will just go back and forth if its uneven, and will only stop when it is all consistent temp, thus reaching thermal equilibrium.
correct me if im wrong
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yeah, if there was a specific time that this happened before equilibrium, then it would be different, but since its at it they both are the same
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the two jars are seperate, thermal equilibrium means the water and the iron are equal in one jar, and the water and the aluminum are equal in the other jar. The two could still be at different temperatures
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in that case i think its the aluminum that is higher because the higher heat capacity means more energy is required to heat the thing, thus more energy is released as it cools. This will heat up the water more than the other one and so when each jar reaches their respective thermal equilibrium points, the one with the aluminum will be higher.
Does this seem to make more sense?
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You can cross out A, cause they will give out heat for different times, because of density and specific heat. You can cross out D and E, because both jars have the same amount and same temperature of water. That leaves you with
B. Iron ball will reach higher final temp than aluminum ball.
C. Aluminum ball will reach higher final temp than iron ball.
I believe that even though aluminum has a higher specific heat,iron is denser, and considering they are put in thermally insulated jars of water (vacuum), the iron will give more heat out into the water for a longer period of time causing the water to be hotter in the end. But since it is a specific heat problem, you could probabaly go with C, because that is what your teacher is looking for
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^you're totally over thinking this
basically, the heat capacity of an element is the amount of joules required to raise it's temperature by 1 degree celsius.
because aluminums heat capacity is twice that of iron (and they are both 80degC) that means that aluminum has twice the amount of joules than iron.
then if they are both put in water jars with the same water conditions, the aluminum will have twice the amount of joules(energy, heat whatever you want to call it) then the iron to give off. so it has to give off a lot more energy to reach thermal equilibrium.
the heat capacities of the waters are the same but the amount of joules added to the water is different - the one with the more joules added will be hotter and that one is aluminum and so the answer is C boooyakashah!!
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ya, that makes more sense
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i was thinking along those lines too, i think im going with C
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THANKS to all the nice folks who provided their insight for me, it is appreciated.
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a, i just had this in physics
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it is final temp of the metal or water
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i just had a test on this and it is c
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thermal equilibrium is reached
ok now you think to yourself...
thermal equilibrium...
doesnt that mean they are all equal in temperature?
then you say oh yea, duh, the answer is
A
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a. they both reach the same temp. think about it. you put some ice and some beer and some water in a cooler. give it a few hours, and they are all the same temp.
now if the question was about how FAST it took to get to the temps, then it'd be different.
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ok, now there are a variety of answers. I am still sticking with my original answer though because:
The higher figure for aluminum means it takes more energy to increase the temp. Since both iron and aluminum are at the same temp, it means that while a certain amount of energy was used to heat up the iron, more was required to get the aluminum to this same point.
When they are then placed into the respective cups of water, they will lose this energy heating up the water. Yes, "thermal equilibrium" means everything is the same temp, but here "everything" means the iron and the water in one jar, and the aluminum and the water in the other [they don't have to equilibrate with eachother!]. Since more energy was used heating up the aluminum, more will be used to heat the water and the resulting equilibrium temp will be higher.
Kapesh?
The beer/water/ice thing isn't a totally applicable analogy. In that example its not a closed system, so ofcourse everything will be the same temp!
I'm not sure if people are getting that they are in two different containers (aren't they?)
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in order to reach an equilibrium all substances must be at the same temp. specific heat has nothing to do with it. the one with the higher specific heat requries more energy to cool it down, thats all.
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I think its a shitty question cause I can't establish whether it is the smae jar
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well it says a "jar" not jars, so assume 1 jar. and its equilibrium, so i too say A
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Yeah if it is just in one jar then the answer is definetly (a) seeing as how that is the definition of Thermal equilibrium. If not, then it is (c).
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a, i havent been in physics for more than half a year and i didnt have to think about it for more than a second, anyone who said other wise has no common sense
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its A 2nd law of thermodynamics says that enerrgy in a container will sperad ot evenly
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gotta be A because they say they are dropped into the same container, so when thermal equilibrium is reached, they will be at the same temperature. so pick A
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in seperate sealed containers, the balls and the water will reach the same temperature eventually (hence equilibrium). But, since the iron ball has a different heat capacity than the aluminum ball, the water (and the balls) will reach different final temperatures in their separate containers. since the jar is a closed system, no outside heat can get in and none of the heat from the inside will escape.
the question either implies separate containers or the mass of the water is that same as the mass of the balls because it says "with the same mass of water".. i'd be willing to bet separate jars
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Haha, i love how this is getting so much attention. Dude, when you get the test back, make sure you let us all know what the answer is!
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Ok, first thing is this is a ski site, but assuming this kid is trying to get the marks to stay in a ski college, I will offer my two cents.
The answer is C, although A seems like a tempting answer. The reason it is not A is because thermal equilibrium is reached by each ball and jar independently of each other, so they are in no way related, so their thermal equilibrium will be different if the balls placed in the jars have different properties, which they do have. The Aluminum has the higher SHC, which just means that it takes more energy to both heat up, and will give off more energy in a cooler environment, and because it give off more energy (heat) the temp of the thermal equilibrium of the jar with the aluminum ball in it will be higher.
I am not currently in physics, so I am not positive about the SHC, so it could be B if I am wrong about what the SHC is, if so, the answer is B.
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