How Is Kinetic Energy Converted to Internal Energy in a Hammer-Spike Collision?

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Homework Help Overview

The discussion revolves around a problem involving the conversion of kinetic energy to internal energy during a collision between a hammer and a spike. The scenario includes a hammer striking a spike, with specific masses and velocities provided, and it is noted that one-third of the kinetic energy is converted to internal energy.

Discussion Character

  • Exploratory, Assumption checking, Problem interpretation

Approaches and Questions Raised

  • Participants discuss the relationship between kinetic energy and internal energy, questioning how to account for the masses involved and which forms of energy can be considered zero. There is exploration of whether potential energy should be included and how to interpret the problem's parameters regarding the hammer and spike.

Discussion Status

The discussion is active, with participants offering insights into the interpretation of the problem. Some guidance has been provided regarding the relationship between kinetic energy and internal energy, and there is an acknowledgment of the need to clarify which mass to use in calculations. Multiple interpretations of the problem are being explored.

Contextual Notes

Participants note that the problem does not specify changes in potential energy and that assumptions about the masses involved may affect the analysis. There is also mention of the lack of explicit details regarding the spike's role in the energy conversion process.

KD
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A worker drives .5 kg spike into a rail tie with 2.50 kg hammer. Hits spike with 65 m/s. 1/3 kinetic energy converted to internal energy. Find increase in total internal energy.

The problem I have having with this problem is that I don't know how to deal with the masses. I know PEi + KEi + Ui = PEf + KEf + Uf. I am having trouble reasoning which ones equal zero.
I'm grateful for any help.
 
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You are looking for the change in Ui. What does the problem tell you about the change in Ui in relation to KE?
 
Ui is 1/3 KEi, right? And KEi is 1/2mv2. But that mass would only be for the hammer. And would the PEf be zero?
 
The problem really doesn't specify that there is a change in potential energy so PEf would be the same as PEi

As far as which kinetic energy to use, my guess would be the hammer unless the problem states otherwise.
 
Would the initial potential energy mgh, have a mass of the spike? Since no distance is mentioned, I'm assuming it is neglible. And then the KEi would be 1/2mv2 with the mass of hammer. + Ui. And that equals mgh with mass of spike? If so, there is no potential energy. Then + .5mv2 with a new velocity using collsion but with mass of...what? Wait a minute. All of these masses has to be the same, doesn't it? I can't go switching between spike and hammer, can I?
 
When dealing with gravitational potential energy you are really only concerned about the change in potential energy because your height is assigned from an arbitrary point.

Unless I am missing something here, the problem is pretty straightforward. It tells you that [tex]\Delta U_{internal} = \frac {1}{3} KE[/tex]. Unless otherwise specified it would be logical to assume that the kinetic energy referred to in the problem is that of the hammer.

It's possible that the KE they're referring to is that of the spike after it's been hit, in which case you would have to use conservation of momentum to find the spike's velocity, and thus kinetic energy.

Can you copy the problem word for word?
 
Okay, I get this problem now. I was making it way more complicated. The spike can be ignored until the final mass and velocity combined witht eh hammer. Thanks for your help, what you said made exact sense. Thanks!
 

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