Heat and phase change: latent heat

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Homework Help Overview

The discussion revolves around a physics problem involving a block of ice undergoing a phase change due to kinetic friction. The scenario includes a 42kg block of ice sliding on a surface, with initial and final speeds provided, and the goal is to determine the mass of ice that melts into water as a result of heat generated by friction.

Discussion Character

  • Exploratory, Conceptual clarification, Mathematical reasoning, Assumption checking

Approaches and Questions Raised

  • Participants discuss the equation relating heat and kinetic energy, questioning the definition of Q and its dimensional consistency. There are attempts to clarify the relationship between kinetic energy lost and heat gained by the ice, with suggestions to refine the equation used.

Discussion Status

The discussion is ongoing, with participants raising questions about the validity of the equations presented and exploring different interpretations of the problem. Some guidance has been offered regarding the relationship between kinetic energy and heat transfer, but no consensus has been reached on the correct formulation.

Contextual Notes

There is a mention of the assumption that the mass of the melted portion of the ice is very small, which may influence the calculations. Participants are also addressing the potential inconsistency in the equations used, indicating a need for clarity in the definitions and relationships involved.

alaa410
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Homework Statement



A 42kg block of ice at 0°C is sliding on a horizontal surface. the initial speed of the ice is 7.3 m/s and the final speed is 3.5m/s. Assume that the part of the block that melts has a very small mass and that all the heat generated by kinetic friction goes into the block of ice. Determine the mass of the ice the melts into water

Homework Equations



Q=mL

The Attempt at a Solution



Q=mL + (1/2v^2 final- 1/2v^2initial)?
 
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alaa410 said:
Q=mL + (1/2v^2 final- 1/2v^2initial)?
What exactly is Q in that equation?
The right hand side is dimensionally inconsistent. It mixes energy and velocity2.
 
q is heat gained or lost; this is the equation they used in the solution so its got to be right...
 
except they multiply not add
 
alaa410 said:
q is heat gained or lost; this is the equation they used in the solution so its got to be right... except they multiply not add
Not exact enough for Q, and the equation would still be nonsensical.
I suggest that the equations ought to say
KE lost = heat gained by ice = mass melted * latent heat of fusion
So now you just need an expression for the KE lost.
 

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