Answer:
the velocity component parallel to the magnetic field vector
Explanation:
When a charged particle moves in a helical path, we can decompose its velocity into two parts v_parallel and v_perpendicular to the magnetic field.
Let's analyze which component receives a force
F = q vxB
the bold letters indicate vectors, in the vector product if the two vectors are parallel the angle is zero and the sin 0 = 0 for which there is no force. therefore the velocity parallel to the field remains constant
If the two vectors are perpendicular, the angle is 90º and the sin 90 = 1, for which there is a force, which has a radial direction and consequently a centripetal acceleration that gives a circular path that does not remove the particle from the magnetic field
When checking the different answers, the correct one is: the velocity component parallel to the magnetic field vector
