The mechanical Equivalent of heat: total increase in temperature of the water?

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Homework Help Overview

The discussion revolves around Joule's paddle wheel experiment, specifically focusing on calculating the total increase in temperature of water when a block falls a certain distance. The subject area includes concepts of mechanical energy, potential energy, and thermal energy.

Discussion Character

  • Exploratory, Conceptual clarification, Mathematical reasoning

Approaches and Questions Raised

  • Participants discuss the formulas for potential energy and thermal energy, questioning how to apply them to the problem. There are inquiries about the values of mass, height, and specific heat capacity, as well as the relationship between potential energy and thermal energy.

Discussion Status

The discussion is active, with participants exploring the relationship between potential energy and thermal energy. Some guidance has been provided regarding the definitions and values needed for calculations, but there is still uncertainty about the interpretation of certain symbols and concepts.

Contextual Notes

Participants express confusion regarding the definition of "J" and its application in the problem, indicating a need for clarification on conceptual understanding and the source of the formulas used.

lalahelp
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Homework Statement


If in Joule's paddle wheel experiment a block of mass 10 kg is allowed to fall through 22.5 meters and the mass of the water is 50 grams. What is the total increase in temperature of the water?



Can your value of J be used for determining how much mechanical energy can be produced from a specified amount of thermal energy?

Homework Equations


Im not sure how to start the problems and do not know what to do could someone please help and explain them to me
 
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What's the formula for potential energy (something with mass and height in it)?
And for thermal energy (something with mass and temperature in it)?
 
PE=mgh
Thermal energy= mct

what do I do from there?
 
Good! :smile:

lalahelp said:
PE=mgh

What would m be in this problem?
And g?
And h?

lalahelp said:
Thermal energy= mct

What would m be in this context?
Do you have a value for c?
How does t fit into your problem?
 
m=10 kg
g=9.8 m/s^2
h=22.5 m
___________
m=50 g
c=4185.8 kg c
t= I am not sure...
 
Right!

Now there is something called conservation of energy.
When your block falls, its potential energy has to go somewhere.
It is converted into heat.
What do you think the relation would be between the potential energy and the thermal energy?

As for "t".
What is it exactly that the problem asks you to calculate?
 
the potential energy equals the thermal energy?
the problem is asking for the total increase in temperature...
 
lalahelp said:
the potential energy equals the thermal energy?

Exactly!

lalahelp said:
the problem is asking for the total increase in temperature...

Yes. And "t" is the symbol for the change in temperature.

So...?
 
ohhh ok i got it Thank you!
could you explain the second question now lol your very helpful
 
  • #10
What is J?
And what are your thoughts on it?
 
  • #11
J is mgh/mct

My book does not say anything about it, it just gives an equation so I am not sure...
 
  • #12
Okay, so you can calculate J, can't you?

Can you put into words what J signifies?
 
  • #13
J means Joules... I thought it was only a unit...
 
  • #14
Yes, J is usually the unit joule of energy.
That's why I asked, because the way J is used in your problem description suggests that J is used for something else...?
Where did your formula for J come from?
 
  • #15
My physics book... its a conceputal problem. Yeh I was confused because it didnt say where that came from.
 
  • #16
Conceptual problem or not, symbols always need to be defined before you can talk about concepts.
Is it defined as the formula you gave then?
 
  • #17
My book says that's how you solve for J, so yes.
 
  • #18
Can you put into words what the formula means then?
 
  • #19
Yes it is defined as the formula
 
  • #20
So what's in the nominator of the formula? And what's in the denominator?
Do you recognize those?
 

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