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

AI Thread Summary
In the discussion about converting kinetic energy to internal energy during a hammer-spike collision, the scenario involves a 2.50 kg hammer striking a 0.5 kg spike at 65 m/s, with one-third of the kinetic energy converted to internal energy. Participants express confusion over how to apply the masses and potential energy in the energy conservation equation. It is clarified that the initial kinetic energy should be calculated using the hammer's mass, while potential energy can be considered negligible due to the lack of height change. The key takeaway is that the change in internal energy is directly related to the hammer's kinetic energy, simplifying the problem significantly. Overall, the discussion emphasizes the importance of correctly identifying which mass and energy types to use in the calculations.
KD
Messages
27
Reaction score
0
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.
 
Physics news on Phys.org
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 \Delta U_{internal} = \frac {1}{3} KE. 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!
 
Back
Top