Posted by Anonymous on Saturday, October 29, 2011 at 4:18pm.
Hello, I'm trying to figure out which of the following statements are TRUE.
I suspect that 2, 6, 8 are true...and that there is one more that is true, but not sure which one?
Thanks!
It is impossible to have a collision between two objects in which the centerofmass of the system is stationary the entire time.
If the magnitude of the momentum of one object is smaller after the collision than it is before the collision, the magnitude of the momentum of the other object must be larger after the collision than it is before the collision.
The vector sum of the momenta of the two objects before the collision equals the vector sum of the momenta of the two objects after the collision.
Momentum and kinetic energy are always conserved.
Momentum and kinetic energy are conserved only when the collision is elastic (when the elasticity equals 1).
The magnitude of the change in momentum for one object in the collision is equal to the magnitude of the change in momentum for the other object in the collision.
The motion of the centerofmass is completely unaffected by any change in the elasticity of a collision.
Momentum is always conserved, but kinetic energy is conserved only when the collision is elastic.
If the centerofmass of the system is moving in one direction before the collision it must move in the opposite direction after the collision.

Physics  Damon, Saturday, October 29, 2011 at 4:24pm
It is impossible to have a collision between two objects in which the centerofmass of the system is stationary the entire time.
1. false
If the magnitude of the momentum of one object is smaller after the collision than it is before the collision, the magnitude of the momentum of the other object must be larger after the collision than it is before the collision.
2. true
The vector sum of the momenta of the two objects before the collision equals the vector sum of the momenta of the two objects after the collision.
3. true
Momentum and kinetic energy are always conserved.
4. false
Momentum and kinetic energy are conserved only when the collision is elastic (when the elasticity equals 1).
5. true
The magnitude of the change in momentum for one object in the collision is equal to the magnitude of the change in momentum for the other object in the collision.
6. true
The motion of the centerofmass is completely unaffected by any change in the elasticity of a collision.
7. true
Momentum is always conserved, but kinetic energy is conserved only when the collision is elastic.
8. true
If the centerofmass of the system is moving in one direction before the collision it must move in the opposite direction after the collision.
9. false 
Physics  kat, Wednesday, October 31, 2012 at 4:20pm
ans above is incorrect, though I don't know what is wrong, just that I got it wrong

Physics  Mike, Sunday, October 20, 2013 at 8:30pm
2 is false

Physics  Sara, Sunday, April 5, 2015 at 8:45pm
It is impossible to have a collision between two objects in which the centerofmass of the system is stationary the entire time.
False
If the magnitude of the momentum of one object is smaller after the collision than it is before the collision, the magnitude of the momentum of the other object must be larger after the collision than it is before the collision.
False
The vector sum of the momenta of the two objects before the collision equals the vector sum of the momenta of the two objects after the collision.
True
Momentum and kinetic energy are always conserved.
False
Momentum and kinetic energy are conserved only when the collision is elastic (when the elasticity equals 1).
True
The magnitude of the change in momentum for one object in the collision is equal to the magnitude of the change in momentum for the other object in the collision.
True
The motion of the centerofmass is completely unaffected by any change in the elasticity of a collision.
True
Momentum is always conserved, but kinetic energy is conserved only when the collision is elastic.
True
If the centerofmass of the system is moving in one direction before the collision it must move in the opposite direction after the collision.
False