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Momentum of two balls

  • Thread starter Herzbog
  • Start date
  • #1
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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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  • #2
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the picture is attached
 
  • #3
Doc Al
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What do you think? What can you say about elastic collision?
 
  • #4
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Ux- Uy = -Vx+Vy

Ux- Uy = -Vx+Vy
I think this is the right equation.
 
  • #5
Doc Al
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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.)
 
  • #6
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The conservation of momentum.
It is elastic collision. Overall speeds are equivalent before and after the collision.
 
  • #7
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Let the direction of Ux be positive and thus that of Vx is negative.
 
  • #8
Doc Al
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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.

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

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