Elastic collision between two moving objects

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Homework Help Overview

The discussion revolves around an elastic collision problem involving two blocks with different masses and initial velocities. The original poster attempts to apply the conservation of momentum and energy principles to determine the final velocities after the collision.

Discussion Character

  • Exploratory, Assumption checking

Approaches and Questions Raised

  • Participants discuss the setup of equations based on conservation laws and question the sufficiency of the given information to solve for the unknown velocities. There is also consideration of how the problem might change if the collision were completely inelastic.

Discussion Status

Some participants acknowledge the original poster's equations as correct but note the lack of necessary information to proceed. The conversation explores the implications of missing data and the nature of the collision.

Contextual Notes

There is a noted absence of the initial velocity of the second block, which is critical for solving the problem. Participants are also considering the differences between elastic and inelastic collisions in their discussions.

captainmustard
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Homework Statement


A 0.2 kg block, moving at 6 m/s, is catching up and colliding elastically with a 0.6 kg block that is moving along the same line and in the same direction. Find the velocities of the ball after this one-dimensional collision.


Homework Equations


Conservation of momentum, conservation of energy


The Attempt at a Solution


First, I figured the momentum and kinetic energy would be conserved so I setup a couple of equations:

m1v1i + m2v2i = m1v1f + m2v2f
and
m1v1i^2 + m2v2i^2 = m1v1f^2 + m2v2f^2

At this point, I realize I have 3 unknowns (v2i, v1f and v2f) and I simply don't know what I can even do with this information. Any ideas at all would be helpful.
 
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Hi, captainmustard. Welcome to PF!

You are right. There is not enough information to answer the question. You have set up the correct equations.
 
Thank you for the response. I thought I was going crazy for a moment there. Would this be possible if it were a completely inelastic collision? I would imagine it would involve some tedious algebra if so.
 
No, you need the initial velocity of the 0.6 kg ball, too.

ehild
 

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