Do Balls X and Y Conserve Momentum and Energy in an Elastic Collision?

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Homework Help Overview

The discussion revolves around the principles of momentum and energy conservation in the context of an elastic collision between two balls, X and Y. Participants are examining the relationships between their velocities before and after the collision.

Discussion Character

  • Conceptual clarification, Assumption checking

Approaches and Questions Raised

  • Participants are exploring various equations that may represent the conservation of momentum and energy in elastic collisions. There are attempts to justify specific equations based on the principles of physics, particularly focusing on the directionality of velocities.

Discussion Status

Some participants have proposed equations and are questioning the reasoning behind them. There is an ongoing exploration of the implications of conservation laws, with hints provided regarding the significance of velocity directions. No consensus has been reached yet.

Contextual Notes

Participants are considering the directions of the velocities as positive or negative, which may affect their interpretations of the equations. The specific details of the collision setup and the values of the velocities are not fully disclosed.

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Two balls X and Y collide elastically. Their speeds before and after collision are as shown.
Before

After
Which of the following equations is correct?

A Ux +Uy = Vx +Vy
B Ux +Uy = Vx - Vy
C Ux - Uy = Vx +Vy
D Ux - Uy = Vx - Vy
 

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What do you think? What can you say about elastic collision?
 
Ux- Uy = -Vx+Vy

Ux- Uy = -Vx+Vy
I think this is the right equation.
 
Why? What's your reasoning? What physics principle or result are you appealing to? (Hint: The directions of the velocities are given; Treat the U's and V's as positive numbers.)
 
The conservation of momentum.
It is elastic collision. Overall speeds are equivalent before and after the collision.
 
Let the direction of Ux be positive and thus that of Vx is negative.
 
Herzbog said:
The conservation of momentum.
It is elastic collision.
Good.
Overall speeds are equivalent before and after the collision.
I don't know what this means. Hint: Conservation of momentum and energy leads to a very specific conclusion about velocities before and after the collision.

Herzbog said:
Let the direction of Ux be positive and thus that of Vx is negative.
OK.
 

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