What is the quantity which is measured by the area occupied below the velocity-time graph?

An object has moved through a distance. Can it have zero displacement? If yes,support your answer with an example.

What can you say about the motion of an object if its speed-time graph is a straight line parallel to the time axis?

The speed-time graph for a car is shown in the figure.
$(a)$ Find how far the car travels in the first $4 \, s$. Shade the area on the graph that represents the distance travelled by the car during this period.
$(b)$ Which part of the graph represents the uniform motion of the car?

$A$ train starting from a railway station and moving with uniform acceleration attains a speed $40 \, km \, h^{-1}$ in $10$ minutes. Find its acceleration (in $m / s^{2}$).

When will you say a body is in $(i)$ uniform acceleration? $(ii)$ nonuniform acceleration?