Projectile Kinetic Energy and Recoil in Spring Gun Experiment

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Homework Help Overview

The discussion revolves around a physics problem involving a projectile fired from a spring gun on a frictionless surface, focusing on the kinetic energy of both the projectile and the recoiling gun. The participants explore concepts related to momentum conservation and kinetic energy calculations.

Discussion Character

  • Exploratory, Conceptual clarification, Mathematical reasoning

Approaches and Questions Raised

  • Participants discuss the conservation of momentum and question the initial momentum of the system. They explore the relationship between the kinetic energies of the projectile and the gun, with some suggesting the use of equations related to kinetic energy and momentum.

Discussion Status

The discussion is active, with participants providing insights into the conservation principles involved. There is a collaborative effort to clarify the relationships between the variables, although no consensus or final solution has been reached.

Contextual Notes

Participants are navigating the constraints of the problem, including the definitions of momentum and kinetic energy, and the implications of the system being initially at rest.

CoreanJesus

Homework Statement


A projectile of mass M1 is fired horizontally from a spring gun that is initially at rest on a frictionless surface. The combined mass of the gun and projectile is M2. If the kinetic energy of the projectile after firing is K, the gun will recoil with a kinetic energy equal to...

Homework Equations


this is part of the problem.
I know you need the kinetic energy formula but I don't get the other formula.

The Attempt at a Solution


N/A Answer is (M1/(M2-M1))K
 
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Hi,

You will need to take into consideration that the total momentum is conserved.
 
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But what should the initial momentum be? 0?
 
Yes, the initial momentum is zero. That does not mean that the final velocity of the gun and of the projectile will be also zero. Do not forget that velocity (and momentum too) is a vector. So if you have two velocities (or momentum) in the opposite directions, you need to subtract one velocity from the other.
 
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so M1V1=(M2-M1)V2
K=.5M1V1^2
KE=.5(M2-m1)V2^2 and plugin?
 
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Exactly.
 
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Thank you so much!
 

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