The displacement of a body in $8\,s$ starting from rest with an acceleration of $20\,cm / s ^2$ is $............$

A student is standing at a distance of $50\,metres$ from the bus. As soon as the bus begins its motion with an acceleration of $1\,ms^{-2}$, the student starts running towards the bus with a uniform velocity $u$. Assuming the motion to be along a straight road, the minimum value of $u$, so that the student is able to catch the bus is.........$ms^{-1}$

A car $A$ is travelling on a straight level road with a uniform speed of $60$$km/h.$It is followed by another car $B$ which is moving with a speed of $70$ $km/h.$When the distance between them is $2.5\, km$, the car $B$ is given a deceleration of $20$$km/{h^2}.$ After how much time will $ B$ catch up with $A$...........$hr$

Two trains travelling on the same track are approaching each other with equal speeds of $40\ m/s$ . The drivers of the trains begin to decelerate simultaneously when they are just $2.0\ km$ apart. Assuming the decelerations to be uniform and equal, the value of the deceleration to barely avoid collision should be..........$m/s^2$