The graph given below is the distance-time graph of an object.
$(i)$ Find the speed of the object during the first four seconds of its journey.
(ii) How long was it stationary?
(iii) Does it represent a real situation? Justify your answer.

(N/A) $(i)$ The segment $OP$ indicates uniform speed.
Speed $v = \frac{\text{Distance}}{\text{Time}} = \frac{75 \ m - 0 \ m}{4 \ s - 0 \ s} = \frac{75}{4} = 18.75 \ m \ s^{-1}$.
(ii) The segment $PQ$ is parallel to the time axis,which indicates that the object is stationary. The duration is from $t = 4 \ s$ to $t = 14 \ s$,so the object was stationary for $14 - 4 = 10 \ s$.
(iii) The segment $QR$ represents a situation where the distance decreases as time increases,which is physically impossible for a single object moving in one dimension. Thus,this does not represent a real situation.