# B Find final velocities after elastic collision

1. Aug 2, 2017

### danred99

Im learming physics through google and I would like to be able to simulate some simple physics prgromatically. Having a hard time with solving for velocites after an elastic collision. Consider two objects, each with a mass of 1kg. One at rest and the other with velocity of 1 m/s in the direction of the first. Although total momentum in the system will be conserved after their collision, it seems there are an infinite number of possible velocities of the two objects after the collision that will satisfy the conservation of momentum; e.g., v1=0.5 m/s and v2=0.5 m/s;
or v1=0.25 m/s and v2=0.75 m/s;
or v1=-0.5 m/s and v2=1.5 m/s;
etc.

What additional piece of information or variable do I need to determine the one outcome in a given circumstance? Is it related to the elasticity of the materials? Is it the amount of time they spend in contact (i.e. impulse)?

2. Aug 2, 2017

### Ignotum per ignotius

If, as you say, the collision is elastic, then (by definition) the sum of the kinetic energies of the two objects remains constant before and after the collision. That's your second constraint.

3. Aug 3, 2017

### danred99

Thanks! guess I'll have to spend more time learning / understanding kinetic energy
Wow! that was simple. now to brush up on my algebra skills

[mentor's note: this post has been lightly edited to fix some auto-correct garbling]

Last edited by a moderator: Aug 4, 2017