Can Kinetic Energy be Substituted for Heat in Latent Heat Calculations?

In summary, the conversation discussed the application of the Q=mc(delta)T equation to determine the mass of ice that melts when a block of copper slides across it. The solution involved making certain assumptions and substituting kinetic energy as the Q value in the latent heat calculation. The importance of making valid assumptions in physics problems was also highlighted.
  • #1
mateomy
307
0
I think I might have a hard time adequately explaining my issue, but here we go…


So everyone knows the Q=mc(delta)T equation, I have this problem that I am working on and it was driving me CRAZY! So I checked out the solutions manual after some time.

Basically the stated a mass of copper was sliding across a slab of ice (Ice, air, and copper were all at 0 degrees Celsius), it said the block eventually comes to rest due to friction. It only gave the mass of the copper (1.60kgs) and the speed (2.50 m/s) and wanted to know the mass of the ice that melted due to the sliding copper. It mentioned looking at the internal energy of the system; both ice and copper, and determining for each what the changes were.

Here's the solution to the first part of the problem…

ScreenShot2011-07-28at20715AM.png


The thing that I am not sure about is substituting the Kinetic value as the Q value as shown in the latent heat calculation. Can you do that? Can you just substitute any energy as the "Q" variable?

Does that make sense? I am on about 15 hours of studying and I think I might be brain-dead.

Thanks.
 
Physics news on Phys.org
  • #2
You can, but only under certain assumptions.

It would seem necessary to assume the following in order to solve the problem as they have done:

- The mass of the ice slab is sufficiently large, such that not all of the ice melts.

- Sublimation (ice -> vapor) does not occur.

- All of the kinetic energy is transformed into heat that is directly or over time indirectly "given" to the ice to cause it to melt (ice -> liquid).

Almost always in physics you have to come up with the right assumptions, and you need to specify why they are good assumptions. It's hard to think of any problem in physics where you don't assume something. This is often the trickiest part of doing physics. Realizing what assumptions you need to make, and why you make them. In this example (your problem), it is wise and perhaps even adequate to assume that all of the kinetic energy is transferred to the surrounding ice and results in the melting of said ice. Although it would be possible to look further into the problem at hand, the results shouldn't deviate that much.

The above assumptions are somewhat good enough to get a rough idea of what happens, and they are valid assumptions as the problem doesn't state specifically the pressure of the surrounding air and other important factors (that would govern the process of sublimation).

I hope this helped! :)
 
  • #3
Definitely helped, thank you.
 

FAQ: Can Kinetic Energy be Substituted for Heat in Latent Heat Calculations?

What is thermodynamics?

Thermodynamics is the branch of physics that deals with the relationships between heat, energy, and work. It studies the behavior of systems in relation to changes in temperature, pressure, and volume.

What is specific heat?

Specific heat is the amount of heat energy required to raise the temperature of a unit mass of a substance by one degree Celsius. It is a characteristic property of a material that reflects its ability to store thermal energy.

How is specific heat measured?

Specific heat is typically measured by conducting a controlled experiment in which a known amount of heat is added to a substance, and the resulting change in temperature is recorded. The specific heat is then calculated using the equation q = mcΔT, where q is the heat added, m is the mass of the substance, c is the specific heat, and ΔT is the change in temperature.

Why is specific heat important?

Specific heat is important because it helps us understand how different materials respond to changes in temperature. It also allows us to calculate the amount of heat needed to achieve a desired change in temperature, which is crucial in fields such as engineering and chemistry.

What are some practical applications of specific heat?

Specific heat has many practical applications, such as in designing heating and cooling systems for buildings, determining the amount of energy needed to cook food, and understanding the effects of temperature changes on the human body. It is also important in fields such as meteorology, geology, and material science.

Back
Top