# What would be the result of this collision?

#### cshum00

-Let's say that in this system particles are only allowed to move in one dimension.
-There are 2 particles moving towards each other.
-Both particles have same mass and velocity.

What will be the result of the inelastic collision?
a) Both particles will come to a stop and no longer move.
b) They will move to the opposite of their original direction with no change in velocity.

I haven't done the math yet but my intuition tells me from the waves behave is that both velocity vectors would cancel each other. But from my knowledge of inelastic condition tells me that their velocity vectors will exchange.

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#### Nick89

(I am assuming you mean a completely inelastic collision??)

Even though the kinetic energy is not conserved in an inelastic collision, there is still conservation of momentum. Can you write out the conservation of momentum?

#### cshum00

Yes, complete inelastic collision.
And let's add that it is a closed system.
So in a closed system, isn't energy supposed to be conserved?

#### rock.freak667

Homework Helper
Yes, complete inelastic collision.
And let's add that it is a closed system.
So in a closed system, isn't energy supposed to be conserved?
If it is a completely inelastic collision then the masses would stick together. So the resultant would be that they both stop using conservation of momentum.

#### Hepth

Gold Member
Yes, complete inelastic collision.
And let's add that it is a closed system.
So in a closed system, isn't energy supposed to be conserved?
If you start calling the "inelastic collision" in a closed system, then you need to define inelastic. Usually it means that any energy transferred to it will sink out into phonons, or some potential somewhere. So really it stays in the system, its just no longer the kinetic energy of the particle. In elastic it would be such that the energy does NOT go into some other form but rather stays as the particles kinetic, and is just transferred.

#### fatra2

So in a closed system, isn't energy supposed to be conserved?
Absolutely. The conservation of energy is "always" true, otherwise you are putting alot of us that studied physics back to square one. Fact is that the energy can change from one form to the other. Therefore, in your system, the kinetic energy is not conserved, but has been transofrmed into another for of energy, which phonon production is very likely, this is not the only possible way.

Cheers