Can a particle be accelerated

$(i)$ if its speed is constant ?

$(ii)$ if its velocity is constant ?

The driver of a train $A$ travelling at a speed of $54\, km h^{-1}$ applies brakes and retards the train uniformly The train stops in $5\, s$. Another train $B$ is travelling on the parallel track with a speed of $36\, km h ^{-1}$. This driver also applies the brakes and the train retards uniformly. The train $B$ stops in $10\, s$. Plot speed time graph for both the trains on the same paper. Also, calculate the distance travelled by each train after the brakes were applied.

Name the physical quantities denoted by

$(i)$ The slope of the distance$-$time graph.

$(ii)$ The area under velocity$-$time graph.

$(iii)$ The slope of velocity$-$time graph.

A scooter starts from rest moves in a straight line with a constant acceleration and covers a distance of $64 \,m$ in $4 \,s$

$(i)$ Calculate its acceleration and its final velocity.

$(ii)$ At what time the scooter had covered half the total distance ?

Can you suggest about the kind of motion of a body from following distance$-$time graphs ?