Please check my work energy required to raise temp by 10degthanks

AI Thread Summary
To heat 1 liter of water by 10 ºC using a mechanical egg beater powered by a 1 kg mass, the energy required is calculated to be 417,915 J. This is derived from the heat capacity of water, where 1 liter equals approximately 55.5 moles, leading to the total energy needed. The work-energy principle is then applied to find the distance the mass must descend, resulting in a calculation of 42.6 meters. However, there is a critical error noted regarding the order of magnitude in the energy calculation, suggesting the need for careful attention to decimal placement. The discussion emphasizes the importance of accuracy in calculations for physics problems.
Dars
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Homework Statement



You want to heat 1 L of water by 10 ºC, and so you heat it with a mechanical egg beater that is powered by a 1 kg mass on a rope over a pulley. How far does the mass have to descend to supply enough work for heating the water?

Homework Equations


|work| = mg(x_f - x_0)
C_P (liquid water) = 75.3JK^-1mol^1


The Attempt at a Solution


I first asked myself how much energy does it take to increase the temp of 1kg of water by 10degC.
Heat capacity of water (above) is the energy required to heat 1 mol of water by 1deg.
So I first determined how many moles of water i have:

1L = 1kg = 1000g * (1mol/18.01g) = 55.5mol of liquid water

Therefore 55.5mol *75.3JK^-1mol^1 = 4179.15J/K * 10K = 417915.0J

So it requires 417915.0J to raise the temp of 1kg water by 10degC.

This is the work required also because work is also in joules, --energy.

Then i used the formula for mechanical work to determine the value for delta x.

|work| = mg(x_f - x_0)

417915.0J(1kJ/10000J) = 1kg(9.81m/s/s)(x_f) (i got ride of x_0 because I set scale so that x_0 = 0)

x_f = 42.6m

So the mass has to descend through 42.6m in order to heat 1kg of liquid water by 10 degC.

Is this correct or if not please help..thanks alot. I also have some other questions about the problem but i don't want to ask until i know if my answer is correct...thank you again
 
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Dars said:
1L = 1kg = 1000g * (1mol/18.01g) = 55.5mol of liquid water
Correct.
Dars said:
Therefore 55.5mol *75.3JK^-1mol^1 = 4179.15J/K * 10K = 417915.0J
"WORNG." Ten x four thousand equals four hundred thousand?
Dars said:
Then i used the formula for mechanical work to determine the value for delta x.
|work| = mg(x_f - x_0)
417915.0J(1kJ/10000J) = 1kg(9.81m/s/s)(x_f) (i got ride of x_0 because I set scale so that x_0 = 0)
x_f = 42.6m
So the mass has to descend through 42.6m in order to heat 1kg of liquid water by 10 degC.
"Four kilometers." You need to pay attention to decimal "orders of magnitude."
 
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