A .5 kg rock is dropped from a height of 20 meters into a pail

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Discussion Overview

The discussion revolves around a physics problem involving a 0.5 kg rock dropped from a height of 20 meters into a pail of water. Participants explore the energy transfer between the rock and the water, specifically focusing on how to calculate the rise in temperature of both the rock and the water based on their specific heats and the potential energy of the rock.

Discussion Character

  • Homework-related
  • Debate/contested
  • Mathematical reasoning

Main Points Raised

  • One participant expresses confusion over the correct approach to solving the problem and requests clarification.
  • Another participant suggests an equation relating the potential energy of the falling rock to the heat gained by both the rock and the water, indicating a belief that the energy of fall should be equated to the heat changes.
  • A different participant argues that the energy changes should be considered in terms of potential energy converting to kinetic energy and then to heat, suggesting that the calculation should focus directly on the heat transfer without needing to calculate kinetic energy.
  • One participant expresses disagreement with the teacher's equation, which includes both the potential energy and the heat of the rock, and seeks help in articulating their perspective.
  • A later reply introduces the assumption that the rock and water may not start at the same temperature, which could affect the heat exchange dynamics between them.

Areas of Agreement / Disagreement

Participants do not reach a consensus on the correct equation to use for the problem. There are competing views regarding the treatment of energy transfers and the initial temperatures of the rock and water.

Contextual Notes

There is uncertainty regarding the initial temperatures of the rock and water, which may influence the heat exchange calculations. Additionally, the participants have not resolved the mathematical steps necessary to arrive at a solution.

Sheldinoh
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My Physics teacher gave us a quiz problem and I don't understand it really how he got his answer. Can you please give me your answer and an explanation for the answer Thanks. Here is the question:

A .5 kg rock is dropped from a height of 20 meters into a pail containing .6 kg of water. The rock has a specific heat of 1480 and the water has a specific heat of 4186. What is the is the rise in temperature of the rock and water ?
 
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Show what you have tried already.
 


I think it is:
mgh(energy of fall ) = mcT + mcT


My teacher says its:
mgh + mcT = mcT
 


.In terms of energy changes PE changes to KE and then to heat in both the water and the rock.It is not necessary to calculate the KE so go straight to your equation which is the correct one.Make sure you plug in the right values for m and c.
 


Thanks for agreeing with me. Could you help me out now with making my physics teacher agree with me. He says that you add the energy of the rock with the heat from the rock to equal the heat of the water. mgh+mcT(rock)=mcT(water). I think it is wrong but I have no clue how to explain it. Do you know how.
 


The impression gained from your question was that the rock and water were both at the same temperature at the start. Let us assume they are not.
If the rock were colder then it would gain some of its heat energy from the heat energy of the water and if the water were colder it would gain some of its heat energy from the heat energy rock.If they were at the same temperature, which is what I assume from your question,then both would gain heat energy from the PE only and both of them would heat up.
 

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