Final answer:
A negatively charged particle moving due east and entering a magnetic field directed due east will be accelerated upward, exhibiting uniform circular motion.
Step-by-step explanation:
When a negatively charged particle is moving at a constant velocity due east and enters a region that has a magnetic field directed due east, the particle will be accelerated upward. This is due to the Lorentz force, which acts perpendicular to both the magnetic field and the velocity of the particle. Since the force is perpendicular to the velocity, it will change the direction of the particle's motion without changing its speed, resulting in uniform circular motion. This corresponds to an acceleration that is directed towards the center of the circular path, which in this case is upwards.