Is it possible for the instataneous velocity to have been negative at any time in the interval suppose the particle started at the origin x 0?

Answer 1

Yes. Since velocity is a vector it can have negative values when the object is moving in the direction opposite to the direction defined as the positive direction.

For example, if an object is thrown vertically upwards and the upward direction is considered the positive direction, then when the object is falling downwards under gravity, its velocity is negative (in the upward direction). Coversely, if the downward direction is defined as the positive direction, then the object has a negative velocity during the first stage of the trajectory.