$(a)$ What is acceleration ? Write its $SI$ unit.

$(b)$ Draw velocity-time graph, when an object has

$(i)$ uniformly accelerated velocity

$(ii)$ uniformly retarded velocity.

The displacement of a moving object in a given interval of time is zero. Would the distance travelled by the object also be zero ? Justify you answer.

Following figure is the speed-time graph for a rocket from the moment when the fuel starts to burn, i.e. at time $t=0$.

$(a)$ State the acceleration of the rocket at $t=0$.

$(b)$ State what happens to the acceleration of the rocket between $t=5 s$ and $t=60 s$.

$(c)$ Calculate the acceleration of rocket at $t=80 s$ Give reason for your answer.

$(d)$ The total mass of the rocket at $t=80\, s$ is $1.6 \times 10^{6}\, kg .$ Calculate the resultant force on the rocket at this time. Give reason for your answer.

A girl running a race accelerates at $2.5\, m s ^{-2}$ for the first $4\, s$ of the race. How far does she travel in this time ?

A body can have zero average velocity but not zero average speed. Justify giving an example.