1. 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 '2 = 41° from the neutron's initial direction. The neutron's initial speed is 5.6 105 m/s. Determine the angle at which the neutron rebounds, '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. Conservation of momentum and conservation of energy 3. I really don't even know how to start with this question. I assume it would have something to do with setting up a conservation of momentum equation then one of energy and solving them both but I'm not sure.