The motion of a charged particle under a constant $\vec{B}$

1. is time-reversal invariant
2. is not time-reversal invariant

The motion of a charged particle under a constant $\vec{B}$

1. conserves the mechanical energy
2. does not conserve the mechanical energy

The work energy “theorem”

The work energy theorem, $\Delta T = W$ where $T$ is the kinetic energy (and $\Delta T = T_2 - T_1$ is its change) and $W$ is the net work done on the particle, is

1. always valid (in classical mechanics).
2. valid only for conservative forces.