Question

When a particle moves on a circle at constant speed, its acceleration vector:

a) is zero m/s^2
b) points toward the center of the circle.
c) points parallel to its velocity vector.

It's zero m/s^2 since it's moving at a constant speed, right?

No. Remember, acceleration is a vector. A vector is something with both magnitude (speed here), and DIRECTION. Although the particle has constant speed, the acceleration is always changing, because the direction is always changing. And that change is pointed toward thte center of the circle.

ok thanks!