When is the acceleration $(i)$ positive and $(ii)$ negative?

Account for the following:
$(a)$ Name the quantity which is measured by the area occupied below the velocity$-$time graph.
$(b)$ Give an example of an object moving in a certain direction with acceleration in the perpendicular direction.
$(c)$ Under what condition is the magnitude of average velocity of an object equal to its average speed?
$(d)$ Give an example of uniformly accelerated motion.
$(e)$ $A$ body is moving along a circular path of radius $r$. What will be the distance and displacement of the body when it completes half a revolution?

The velocity$-$time graph of a truck is plotted below.
$(a)$ Calculate the magnitude of displacement of the truck in $15$ seconds.
$(b)$ During which part of the journey was the truck decelerating?
$(c)$ Calculate the magnitude of average velocity of the truck.

Answer the following questions:
$(i)$ State the type of motion shown by a freely falling stone.
$(ii)$ When a stone is thrown vertically upwards,its velocity is continuously decreased. Why?
$(iii)$ Give an example of a motion in which average velocity is zero,but the average speed is not zero.

Starting from rest at the top of an inclined plane, a body reaches the bottom of the inclined plane in $4$ seconds. In what time does the body cover one-fourth of the distance starting from rest at the top?

The direction of acceleration of an object moving in a circular path is