A motorcyclist drives from $A$ to $B$ with a uniform speed of $30\, km\, h^{-1}$ and returns back with a speed of $20 \,km \,h^{-1}$. Find its average speed(in $km\, h^{-1}$).

A girl of mass $50\, kg$ jumps out of a moving boat of mass $300\, kg$ on to the bank with a horizontal velocity of $3\, m s ^{-1}$. With, what velocity, does the boat begin to move backwards ?

An aeroplane lands at $216\, km\, h ^{-1}$ and stops after covering a runway of $2\, km .$ Calculate the acceleration and the time, in which its comes to rest.

Define velocity.

How can you find the following ?

$(i)$ Velocity from a displacement$-$time graph.

$(ii)$ Acceleration from velocity$-$time graph.

$(iii)$ Displacement from velocity$-$time graph.

$(iv)$ Velocity from acceleration$-$time graph.