Physics
posted by Ben .
A neutron collides elastically with a helium nucleus (at rest initially) whose mass is four times that of the neutron. The helium nucleus is observed to rebound at an angle θ'2 = 44° from the neutron's initial direction. The neutron's initial speed is 7.0 105 m/s. Determine the angle at which the neutron rebounds, θ'1, measured from its initial direction.
What is the speed of the neutron after the collision?
What is the speed of the helium nucleus after the collision?

You will have to write and solve three conservation equations (x momentum, y momentum, and kinetic energy) to solve for the three unknowns (2 final speeds and exit angle). It is often easiest to do this in a coordinate system that moves with the center of mass and then translate back to laboratory coordinates. This would take about a page of calculations and I do not have time to do it for you.