Thermodynamics B/C

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WhatScience?
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Thermodynamics B/C

Postby WhatScience? » September 1st, 2017, 9:36 am

Welcome to 2018 Thermodynamics!

A heat engine has a thermal efficiency of 45%. How much power does the engine produce when heat is transferred into it at 10^9 kJ/Hr?

Please give your answer in the unit MW.
"When you clean your room, you are increasing the total chaos of the universe" - Hank Green Crash Course (Entropy)

Events 2018

Thermodynamics, Potions and Poisons, Disease Detectives, Optics, and Towers

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Re: Thermodynamics B/C

Postby daydreamer0023 » September 2nd, 2017, 7:18 am

Welcome to 2018 Thermodynamics!

A heat engine has a thermal efficiency of 45%. How much power does the engine produce when heat is transferred into it at 10^9 kJ/Hr?

Please give your answer in the unit MW.
Is this correct?
Answer
12.5 MW
"I am among those who think that science has great beauty. A scientist in his laboratory is not only a technician: he is also a child placed before natural phenomena which impress him like a fairy tale." - Marie Curie

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Re: Thermodynamics B/C

Postby WhatScience? » September 2nd, 2017, 8:06 am

Welcome to 2018 Thermodynamics!

A heat engine has a thermal efficiency of 45%. How much power does the engine produce when heat is transferred into it at 10^9 kJ/Hr?

Please give your answer in the unit MW.
Is this correct?
Answer
12.5 MW
No, but close
Answer
125 MW. Conversion from joules to MW is 3,600,000 to 1.
"When you clean your room, you are increasing the total chaos of the universe" - Hank Green Crash Course (Entropy)

Events 2018

Thermodynamics, Potions and Poisons, Disease Detectives, Optics, and Towers

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daydreamer0023
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Re: Thermodynamics B/C

Postby daydreamer0023 » September 3rd, 2017, 12:16 pm

Probably missed a decimal place on my part somewhere down the line in calculations...oh well. Next question:

How do state variables differ from path functions? Give two thermodynamics related example of each.
"I am among those who think that science has great beauty. A scientist in his laboratory is not only a technician: he is also a child placed before natural phenomena which impress him like a fairy tale." - Marie Curie

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Re: Thermodynamics B/C

Postby WhatScience? » September 3rd, 2017, 12:50 pm

Answer
A state variable is a change that is dependent only on the initial and final states. A path variable is a variable that depends on the process from final to initial- the path. A physics example of a state variable would be ΔU (change in internal energy) A physics example of a path variable would be ΔQ (change in heat). A real world scenario of a state and variable would be something like this: Let us say that a bodybuilder wants to lift a weight 100 times. Either way he will do a 100 lifts. So the amount of lifts is a state variable. However, the weight of the weight could change. Depending on the weight he is lifting, be it 1 pound or a 100 pounds, the amount of energy he spends will change, making expended energy a path variable.
"When you clean your room, you are increasing the total chaos of the universe" - Hank Green Crash Course (Entropy)

Events 2018

Thermodynamics, Potions and Poisons, Disease Detectives, Optics, and Towers

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Re: Thermodynamics B/C

Postby daydreamer0023 » September 4th, 2017, 10:19 am

Answer
A state variable is a change that is dependent only on the initial and final states. A path variable is a variable that depends on the process from final to initial- the path. A physics example of a state variable would be ΔU (change in internal energy) A physics example of a path variable would be ΔQ (change in heat). A real world scenario of a state and variable would be something like this: Let us say that a bodybuilder wants to lift a weight 100 times. Either way he will do a 100 lifts. So the amount of lifts is a state variable. However, the weight of the weight could change. Depending on the weight he is lifting, be it 1 pound or a 100 pounds, the amount of energy he spends will change, making expended energy a path variable.
Looks correct to me. :) Your turn.
"I am among those who think that science has great beauty. A scientist in his laboratory is not only a technician: he is also a child placed before natural phenomena which impress him like a fairy tale." - Marie Curie

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Re: Thermodynamics B/C

Postby WhatScience? » September 4th, 2017, 2:00 pm

A person wants to replace the window on their house, but they don't want their heating and cooling bills to change. The original window on the wall of the house has area A, thickness d, and is made out of glass that has a thermal conduction constant k. Which one of the following changes could be made to the window that would leave the rate of thermal conduction the same as the original window?

A: double the area, cut the thickness in half, cut the k constant in half

B: cut the area in half, cut the thickness in half, and double the k constant

C: quadruple the area, double the thickness, cut the k constant in half

D: double the area, double the thickness, quadruple the k constant
"When you clean your room, you are increasing the total chaos of the universe" - Hank Green Crash Course (Entropy)

Events 2018

Thermodynamics, Potions and Poisons, Disease Detectives, Optics, and Towers


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