I will assume that horizontal axis is for the time t, vertical axis is for position y.


(a)  Velocity is zero where the derivative    is zero.

     They are the points, where the tangent line to the plot is horizontal.

     These points are B, D, E, G, I, J.  


(b)  The acceleration is zero where the second derivative  is zero.
     These points are the inflection points.

     In the plot, they are C, E, H, and some point between I and J,  which 
     is not marked in the plot.


(c)  These intervals are BC, DF, GH, IJ.

     These intervals are those where the position y of the object becomes closer 
     to zero as the time increases.

     
(d)  The acceleration is negative where the plot is convex upwards (arcs CDE, HIJ).

     The velocity is negative where the derivative   is negative
     (Arcs AB, DEFG, IJ).

     Both the acceleration is negative and the velocity is negative in intersections 
     of these sets/arcs DE and IJ.


(e)  Regarding first 2.5 seconds, 
     the body starts (t=0) from the detector position and moves in the "negative"
     direction from the detector until getting point B on the graph.
     At the start, the starting velocity is negative. 
     On the curve AB, acceleration is positive, so the magnitude 
     of the velocity diminishes and the negative velocity steadily 
     becomes 0 at point B.

     After getting point B, the body moves to the detector (curve BC) with positive acceleration,
     passes the detector, and further moves from the detector in "positive" direction.
     Curve CD describes decelerated movement. The velocity on CD remains positive, 
     but the magnitude of the velocity steadily diminishes.
     At point D, the velocity becomes zero, and the body starts moving to the detector.


     At this point, I will stop my story to leave the room for you to think and to describe 
     the further events on your own.