If the displacement of a body is proportional to the time elapsed,what type of motion does the body possess?

The speed-time graph of a body is a straight line parallel to the time axis. The body has:

$A$ body moves with a velocity of $2\, m s^{-1}$ for $5\, s$,then its velocity increases uniformly to $10\, m s^{-1}$ in the next $5\, s$. Thereafter,its velocity begins to decrease at a uniform rate until it comes to rest after $5\, s$.
$(i)$ Plot a velocity-time graph for the motion of the body.
$(ii)$ From the graph,find the total distance covered by the body after $2\, s$ and $12\, s$.

By giving an example,prove that rest and motion are relative terms.

$A$ cyclist goes once around a circular track of diameter $105 \, m$ in $5 \, minutes$. Calculate his speed. (in $m/s$)

$(a)$ What is acceleration? Write its $SI$ unit.
$(b)$ Draw velocity-time graphs for an object having:
$(i)$ Uniformly accelerated velocity.
$(ii)$ Uniformly retarded velocity.