Final answer:
A proton at rest in a uniform electric field will accelerate and convert its electric potential energy into kinetic energy, moving in a straight line with uniformly accelerated motion.
Step-by-step explanation:
When a proton is placed at rest in a uniform electric field and then released, it will begin to accelerate in the direction of the electric field if the field is pointing away from the proton, or in the opposite direction if the field is pointing towards the proton. This is due to the fact that protons are positively charged particles and are attracted to areas of negative electric potential. As the proton accelerates, it gains kinetic energy at the expense of its electric potential energy. Therefore, throughout its motion in the electric field, the total energy of the proton remains constant (assuming no external forces are involved), but there is a conversion occurring between potential and kinetic forms of energy. The motion of the proton will be uniformly accelerated in a straight line until other forces come into play or until it strikes another object.