Elastic Collision between a neutron and helium nucleus.

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1. The problem statement, all variables and given/known data

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 = 41° from the neutron's initial direction. The neutron's initial speed is 6.2 x10^5 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?

2. Relevant equations

conservation of momentum
conservation of energy

3. The attempt at a solution

Wound up with a very messy system of equations involving conservation of momentum in both the x and y directions as well as conservation of energy. Any help would be greatly appreciated!
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Can you show some details of what you did? Then perhaps someone will be able to find if you did go wrong and where.

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