I am stuck on 3 questions =/

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In summary, the first conversation discusses heat transfer and the final temperature of a copper slug, beaker, and water when thermal equilibrium is reached. The second conversation explores how to make ice without a refrigerator using radiation, while the third conversation applies the ideal gas law to calculate the final pressure of oxygen in a cylinder after a change in temperature and volume.
  • #1
Goalcard
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1. Heat Transfer
A copper slug whose mass mc is 75g is heated in a laboratory oven to a temperature T of 3120C. The slug is then dropped into a glass beaker containing a mass mw =220g of water. The heat capacity Cb of the beaker is 45 cal/K. The initial temperature Ti of the water and the beaker is 120C. What is the final temperature Tf of the slug, the beaker, and the water when thermal equilibrium is reached?

Would this look about right?
mc(water)+mc(copper calorimeter) +mc (beaker) = 0.

2. How to Make Ice Without a Refrigerator
On a clear moonless night, the sky acts like a blackbody radiator at a temperature Ts=
-230 C. You thermally insulate a container from the ground (by placing a poorly conducting layer of straw beneath it). Then you pour water into the container, forming a thin, uniform layer with mass m=4.5 g, with surface area A = 9.0 cm2 and depth= 5.0 mm. The emissivity is .9, and initial temperature 6.00C. Find the time required for the water to freeze via radiation.

On this one I am super lost, no idea from where to start.

3. The Ideal Gas Law
A cylinder contains 12 L of oxygen at 200C and 15 atm. The temperature is raised to 350C, and the volume is reduced to 8.5 L. What is the final pressure of the gas in atmospheres?

Same as the other one, if you guys/gals can point me to the right direction formula wise that would be great.
 
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  • #2
I didn't have time to read 1 and 2 but for 3 you should be able to use

intial PV/T = final PV/T
 
  • #3
Hermite said:
I didn't have time to read 1 and 2 but for 3 you should be able to use
intial PV/T = final PV/T
Does this look about right?
P(12)/200=P(8.5)/350
 
  • #4
Goalcard said:
Does this look about right?
P(12)/200=P(8.5)/350

yes no maybe so? :biggrin:
 
  • #5
you're on the right track.. How about including your initial pressure [itex]P_i[/itex] and solving for final pressure [itex]P_f[/itex]
 
  • #6
Ouabache said:
you're on the right track.. How about including your initial pressure [itex]P_i[/itex] and solving for final pressure [itex]P_f[/itex]
final pressure would be 37.059?
 
  • #7
Goalcard said:
final pressure would be 37.059?
Yeah? any tips on the first two?
 
  • #8
Goalcard said:
Yeah? any tips on the first two?
Maybe throw me a formula, that would help me a lot, it's due tomorrow(Wednesday)
 
  • #9
Goalcard said:
final pressure would be 37.059?
Looks good to me..

On the first two, if I were assigned these questions, instead of guessing which formula to use, I would review material on heat transfer and black body radiation. Here is a starting point ref
 

1. How can I come up with a solution to the first question?

The best way to approach this is to break down the question into smaller parts and gather all the information and data you have. Then, try to think outside the box and consider different perspectives or methods to solve the problem.

2. What if I don't have enough information to answer the second question?

In science, it is common to encounter situations where there is limited or incomplete data. In this case, you can try to make logical assumptions or use mathematical models to fill in the missing information. You can also conduct further research or experiments to gather more data.

3. I don't understand the third question. How can I clarify it?

If the question is unclear or confusing, it is best to reach out to the person who posed the question and ask for clarification. You can also consult with other experts in the field or refer to credible sources for more information.

4. What if I get stuck and can't find a solution to any of the questions?

It is important to remember that not all problems have immediate solutions. In these situations, it is best to take a step back and approach the questions from a different angle. You can also consult with colleagues or take a break and come back to the questions with a fresh perspective.

5. Can I collaborate with others to solve these questions?

Yes, collaboration is an essential part of the scientific process. Working with others can bring new insights and perspectives, and help you find solutions to complex problems. Just be sure to give credit to all collaborators and follow proper research ethics and protocols.

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