Proceeding from the fundamental equation of relativistic dynamics, find: (a) under what circumstances the acceleration of a particle coincides in direction with the force \(\mathbf{F}\) acting on it; (b) the proportionality factors relating the force \(\mathbf{F}\) and the acceleration \(\mathbf{w}\) in the cases when \(\mathbf{F} \perp \mathbf{v}\) and \(\mathbf{F} \| \mathbf{v},\) where \(\mathbf{v}\) is the velocity of the particle.