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

1. Nov 30, 2011

### lalahelp

1. The problem statement, all variables and given/known data
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?

2. Relevant 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

2. Nov 30, 2011

### I like Serena

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)?

3. Nov 30, 2011

### lalahelp

PE=mgh
Thermal energy= mct

what do I do from there?

4. Nov 30, 2011

### I like Serena

Good!

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

What would m be in this context?
Do you have a value for c?
How does t fit into your problem?

5. Nov 30, 2011

### lalahelp

m=10 kg
g=9.8 m/s^2
h=22.5 m
___________
m=50 g
c=4185.8 kg c
t= Im not sure...

6. Nov 30, 2011

### I like Serena

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?

7. Nov 30, 2011

### lalahelp

the potential energy equals the thermal energy?
the problem is asking for the total increase in temperature...

8. Nov 30, 2011

### I like Serena

Exactly!

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

So...?

9. Nov 30, 2011

### lalahelp

ohhh ok i got it Thank you!

10. Nov 30, 2011

### I like Serena

What is J?
And what are your thoughts on it?

11. Nov 30, 2011

### lalahelp

J is mgh/mct

My book does not say anything about it, it just gives an equation so im not sure...

12. Nov 30, 2011

### I like Serena

Okay, so you can calculate J, can't you?

Can you put into words what J signifies?

13. Nov 30, 2011

### lalahelp

J means Joules... I thought it was only a unit...

14. Nov 30, 2011

### I like Serena

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. Nov 30, 2011

### lalahelp

My physics book... its a conceputal problem. Yeh I was confused because it didnt say where that came from.

16. Nov 30, 2011

### I like Serena

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. Nov 30, 2011

### lalahelp

My book says thats how you solve for J, so yes.

18. Nov 30, 2011

### I like Serena

Can you put into words what the formula means then?

19. Nov 30, 2011

### lalahelp

Yes it is defined as the formula

20. Nov 30, 2011

### I like Serena

So what's in the nominator of the formula? And what's in the denominator?
Do you recognize those?