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

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.

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

A train starting from rest picks up a speed of $10\, m s ^{-1}$ in $100\, s$. It continues to move at the same speed for the next $250\, s$. It is then brought to rest in the nert $50\, s$. Plot a speed$-$time graph for the entire motion of the train.

$(i)$ acceleration of the train while accelerating,

$(ii)$ retardation of the train while retarding,

$(iii)$ and the total distance covered by the train.

From the given $v -t$ graph (Fig.), it can be inferred that the object is