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Physics/Finding final temperature of mix


QUESTION: Hello, Mr. Nelson! I am going to take a physics test in 2 days and have to turn in the guide tomorrow, and I was really hoping you might be able to help me out on this one. I can't understand how to do it and would be very grateful if you could explain so I will know how to do it for the test the day after tomorrow!
Thank you in advance!

Specific heat of alcohol: 0.6 cal/gC
Mass of alcohol: 800g
Initial temperature of alcohol: 50C
Specific heat of water: 1 cal/gC
Mass of water: 3,000g
Initial temperature of water: 17C
Specific heat of glass: 0.199 cal/gC
Mass of glass: 400g
Initial temperature of glass: 17C

How do I find the final temperature of the mix?

ANSWER: First, you take notes and study hard all semester long.  Then you conserve energy, energy out of each of the initial products equals the energy of all the products combined.  Simple.  If you need more than that, study harder, because this appears to be homework.

---------- FOLLOW-UP ----------

QUESTION: I am sorry if I have offended you, Mr. Nelson. I have studied hard. Physics is just very difficult for me, and the teacher has explained multiple times and I still don't get it. I'm an A+ student in all other subjects, including math (I don't mean to brag, just stating the truth!) and I get along very well with all of my teachers because of my responsibility.
I have been hacking at this problem for hours and can't seem to get it right. It is not for homework, but rather part of the guide for the test I have tomorrow.
Thank you.

No, you don't understand, I told you how to solve the problem.  Conserve energy.  The heat out of the hot things equals the heat into the colder things.  Heat is a form of energy (the first law of thermodynamics).  So just set the heats out (mass*specific heat*change in temperature) equal to the heats in (same thing). You use T_initial-T_final to make the change in temperature and solve (there's a minus sign for out vs. in).  T_final is the only unknown.  Simpler than you're making it.


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Dr. Stephen O. Nelson


I can answer most basic physics questions, physics questions about science fiction and everyday observations of physics, etc. I'm also usually good for science fair advice (I'm the regional science fair director). I do not answer homework problems. I will occasionally point out where a homework solution went wrong, though. I'm usually good at explaining odd observations that seem counterintuitive, energy science, nuclear physics, nuclear astrophysics, and alternative theories of physics are my specialties.


I was a physics professor at the University of Texas of the Permian Basin, research in nuclear technology and nuclear astrophysics. My travelling science show saw over 20,000 students of all ages. I taught physics, nuclear chemistry, radiation safety, vacuum technology, and answer tons of questions as I tour schools encouraging students to consider careers in science. I moved on to a non-academic job with more research just recently.

Ph. D. from Duke University in physics, research in nuclear astrophysics reactions, gamma-ray astronomy technology, and advanced nuclear reactors.

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