Gun-projectile Elastic Collisions

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Discussion Overview

The discussion revolves around a physics problem regarding the muzzle speed of a projectile when fired from a gun that is free to recoil. Participants explore the conservation of momentum and kinetic energy in this context, while addressing the challenges of solving for two unknown variables: the new speed of the projectile and the recoil speed of the gun.

Discussion Character

  • Homework-related
  • Exploratory
  • Technical explanation

Main Points Raised

  • One participant describes a problem involving the muzzle speed of a projectile and the conditions under which the gun recoils freely, noting the challenge of having two variables in the equations.
  • Another participant emphasizes the conservation of momentum as a fundamental principle relevant to the problem.
  • There are suggestions to create equations based on momentum and kinetic energy to approach the problem.
  • Participants discuss the technical difficulties of posting in the Homework Help forums, indicating a potential bug with the mobile app.
  • One participant expresses uncertainty about how to relate momentum and kinetic energy in the context of the problem.

Areas of Agreement / Disagreement

Participants generally agree on the conservation of momentum being a key principle, but there remains uncertainty regarding the relationship between momentum and kinetic energy, as well as how to effectively solve the problem with the given variables.

Contextual Notes

Participants note the need for simultaneous equations to relate momentum and kinetic energy, but the specific mathematical steps and assumptions required to solve the problem remain unresolved.

Who May Find This Useful

This discussion may be useful for students encountering similar problems in physics related to projectile motion and conservation laws, particularly in the context of recoil and elastic collisions.

Calvin Pitts
So I'm reading my textbook and there's a problem asking what the muzzle speed of a projectile would be if the gun it is being fired from is free to recoil. I'm given the muzzle speed of the projectile when the gun is stationary, the mass of the projectile, and the mass of the gun. I'm also told that the kinetic energies of the system is the same for both cases. How is a problem like this solved? Every equation I've thought of so far ends up with two variables (the projectile's new speed and the gun's free-to-recoil speed).
 
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Calvin Pitts said:
So I'm reading my textbook and there's a problem asking what the muzzle speed of a projectile would be if the gun it is being fired from is free to recoil. I'm given the muzzle speed of the projectile when the gun is stationary, the mass of the projectile, and the mass of the gun. I'm also told that the kinetic energies of the system is the same for both cases. How is a problem like this solved? Every equation I've thought of so far ends up with two variables (the projectile's new speed and the gun's free-to-recoil speed).
Welcome to the PF. :smile:

When there are no outside forces involved (when the gun is free to recoil), what fundamental quantities are conserved?
 
berkeman said:
Welcome to the PF. :smile:

When there are no outside forces involved (when the gun is free to recoil), what fundamental quantities are conserved?
Momentum is conserved.
 
BTW, once you get the fundamental concepts involved, you can start a thread about the problem in the Homework Help, Introductory Physics forum, and fill out the Template that you are provided there. You can show your work on the problem, and ask us to check it for you. :smile:
 
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berkeman said:
BTW, once you get the fundamental concepts involved, you can start a thread about the problem in the Homework Help, Introductory Physics forum, and fill out the Template that you are provided there. You can show your work on the problem, and ask us to check it for you. :smile:
Awesome, thanks for letting me know!
 
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Calvin Pitts said:
Momentum is conserved.
Great! So go ahead and start the thread in the HH forums, and show how you work out the problem using that information. Go ahead and post a link to your new thread here once you've started it.
 
Create one equation using momentum, and another with kinetic energy.
 
scottdave said:
Create one equation using momentum, and another with kinetic energy.
Good hints. Let's see what he posts in his HH thread. Thanks.
 
berkeman said:
Good hints. Let's see what he posts in his HH thread. Thanks.
I'm spending as much time trying to figure out how to post on the thread as I am trying to figure out the problem. Haha I'm using an iPhone right now, which always seems to make my life harder :)
 
  • #10
Oh rats. There may be a bug that keeps you from being able to post in the Homework Help forums using the PF app right now, sorry about that.. Can you post from a laptop or desktop later, or just use the web to post it? Ack!
 
  • #11
berkeman said:
Oh rats. There may be a bug that keeps you from being able to post in the Homework Help forums using the PF app right now, sorry about that.. Can you post from a laptop or desktop later, or just use the web to post it? Ack!
I'm actually just using the web browser on my phone. Haha I think I can post, it just takes a while to get there. I'm having more trouble figuring out the problem now. Because I'm not exactly sure how to relate momentum and kinetic energy.
 
  • #12
Calvin Pitts said:
. Because I'm not exactly sure how to relate momentum and kinetic energy.
The hint was to use those for two simultaneous equations...
 
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  • #13
I'll go ahead and close this thread in the technical forums so you can start your thread in the Homework Help forums. :smile:
 
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