A hydrogen molecule, mass 2.00u and velocity 1.88x 10^3 m/s, collides elastically and head-on with an oxygen m

Question

a hydrogen molecule, mass 2.00u and velocity 1.88x 10^3 m/s, collides elastically and head-on with an oxygen molecule, mass 32.0u and velocity 405m/s. The hydrogen molecule is moving to the right and the oxygen molecule is moving to the left in a straight plane.
(a) determine the velocity of seperation of the two molecules after the collision
(b) apply the law of conservation of momeentum to the collision
(c) determine the velocity of both molecules after the collision

Answer 1

Sounds like a homework problem to me. I won't do the work for you, but I will point you in the right direction.
This is a classic conservation of momentum problem. The total momentum of the two objects before the collision must equal the total momentum of the two objects after the collision. That is to say:
before(m1v1+m2v2) =after(m1v1+m2v2)
you know the before masses and velocities. And since the problem says that it is an "elastic" collision, then no energy is lost to heat, sound, etc. The masses of the two particles remains unchanged, so only the velocities are changed.
Warning: mind your directions and signs (+/-). Hydrogen is a very light atom compared to oxygen. Most likely the hydrogen atom will "bounce" back the way it came and the oxygen atom will just slow down a bit.
to get part (a), just subtract the two velocities after the collision

The problem can also be solved using a conservation of energy solution, but why make it harder than it needs to be?