Each of the three graphs represents acceleration versus time for an object that already has a positive velocity at time $t_1$. Which graphs show an object whose speed is increasing for the entire time interval between $t_1$ and $t_2$ ?

A motor car moving at a speed of $72\, km/h$ cannot come to a stop in less than $3.0\,\sec $ whilefor a truck this time interval is $5.0\,\sec $. On a highway, the car is behind the truck  both moving at $72\, km/h$. The truck gives a signal that it is going to stop at emergency. At what distance the car should be from the truck so that it does not bump onto (collide with) the truck. Human response time is $0.5\,\sec $.

When acceleration and average acceleration are equal for moving object ?

The area under acceleration-time graph gives

The acceleration of a moving body can be found from

For the acceleration-time $(a-t)$ graph shown in figure, the change in velocity of particle from $t=0$ to $t=6 \,s$ is ........ $m / s$