The posttion of an object moving along $x$ -axis ts given by $x=a+b t^{2}$ where $a=8.5\; \mathrm{m}, b=2.5 \;\mathrm{m} \mathrm{s}^{-2}$ and $t$ is measured in seconds. What is the average velocity between $t=2.0 \;\mathrm{s}$ and $t=4.0 \;\mathrm{s} ?$

A bus travelling the first one-third distance at a speed of $10\; km/h$, the next one-third at $20\; km/h$ and at last one-third at $60\; km/h$. The average speed of the bus is …….. $km/h$

The average velocity of a body moving with uniform acceleration travelling a distance of $3.06\, m$ is $ 0.34 ms^{-1}$. If the change in velocity of the body is $ 0.18ms^{-1}$ during this time, its uniform acceleration is………$ms^{-2}$

A car moves a distance of $200 \;m$. It covers the first half of the distance at speed $40 \;km / h$ and the second half of distance at speed $v$. The average speed is $48\; km / h$. The value of $v$ is

A car travels a distance $S$ on a straight road in two hours and then returns to the starting point in the next three hours. Its average velocity is