Задача id12682

A neutron experiences an elastic collision with a helium nucleus and then, having been reflected, elastically collides with another helium nucleus (in elastic collisions, the total kinetic energy is conserved). The helium nuclei were motionless before the collision. Considering both collisions to be central (i.e., the velocities before and after the collision are directed along the line of the centers of the colliding particles), determine how many times the neutron energy will change after two collisions.

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