A charged particle enters an environment of a strong and non-uniform magnetic field varying from point to point both in magnitude and direction and comes out of it following a complicated trajectory. Would its final speed equal the initial speed if it suffered no collisions with the environment?
The magnetic field present in the region affects the direction of motion of the particle but it doesn't affect the magnitude of the speed of the particles. So, it is fairly possible that the particle comes out with the same speed as the initial speed with which it enters the field.
