Posted by **Mina** on Wednesday, November 28, 2012 at 7:23pm.

What happens after an elastic collision between a hydrogen atom at rest and a helium atom moving 150 m/s? Which direction will the particle move after the collision? Which particle will have a higher speed after the collision? What happens when a neutron moving at 150 m/s hits a hydrogen atom at rest?

- Physics -
**Jennifer**, Thursday, November 29, 2012 at 2:13pm
For an elastic collision, both kinetic energy and momentum are conserved.

Conservation of momentum

m(He)*v(He,initial) = m(He)*v(He,final) + m(H)*v(H)

where m(He) is the mass of the Helium,

v(He, inital) is the initial speed of the Helium , etc. . .

Conservation of kinetic energy:

0.5*m(He)*v(He,initial)^2 = 0.5*m(He)*v(He,final)^2 + m(H)*v(H)^2

you should be able to look up the masses of a hydrogen atom and a helium atom. Then, you have two equations with 2 unknowns (v(He, final) and v(H)). You can use algebra to solve for these two values.

For the second part, repeat this problem by replacing the helium with a neutron.

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