Final answer:
The angular position that does not describe a particle stopping on the positive y-axis is π radians as it corresponds to the negative y-axis. The other options are coterminal with π/2 radians and do describe the particle stopping on the positive y-axis.
Step-by-step explanation:
The student's question is related to angular position in circular motion, specifically which of the given options does not describe the particle's angular position when it stops on the positive y-axis. In a circular path in the xy plane, the positive y-axis corresponds to an angular position of π/2 radians (90 degrees). Option B, π radians, corresponds to the negative y-axis, and thus does not describe a particle stopping on the positive y-axis. Option C, 5π/2 radians, and option D, -3π/2 radians, are coterminal angles with π/2 radians, and they do describe a particle stopping on the positive y-axis, as they are equivalent to one full revolution plus π/2 radians, and negative one full revolution plus π/2 radians, respectively. Therefore, the angular position that does not describe the particle stopping on the positive y-axis is option B, π radians.