$A$ person standing at $A$ goes to $B$ by following any of the paths $1, 2$ or $3$. Which path can we measure to find the average velocity?

$(a)$ Differentiate acceleration from velocity.
$(b)$ Can a body have acceleration without change in magnitude of velocity? Explain with an example.
$(c)$ $A$ motor boat starting from rest on a lake accelerates in a straight line at a constant rate of $3 \, m s^{-2}$ for $8 \, s$. How far does the boat travel during this time?

Give examples to distinguish:
$(i)$ Distance and displacement.
$(ii)$ Speed and velocity.
$(iii)$ Acceleration and retardation.

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 the speed-time graph for both the trains on the same paper. Also,calculate the distance travelled by each train after the brakes were applied.

Can a particle be accelerated
$(i)$ if its speed is constant?
$(ii)$ if its velocity is constant?

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.