Which one of the following represents the displacement-time graph of two objects $A$ and $B$ moving with zero relative velocity?

The area under an acceleration-time graph gives:

The displacement-time graph of two moving particles makes angles of $30^{\circ}$ and $45^{\circ}$ with the time axis ($X$-axis). The ratio of their velocities is

Two trains, which are moving along different tracks in opposite directions, are put on the same track by mistake. On noticing the mistake, when the trains are $300 \, m$ apart, the drivers start slowing down the trains. The graphs given below show the decrease in their velocities as a function of time. The separation between the trains when both have stopped is: (in $ \, m$)

The displacement-time graph of a moving particle is shown below. The instantaneous velocity of the particle is negative at the point:

The diagram shows the variation of $1/v$ (where $v$ is the velocity of the particle) with respect to time $t$. Using the details given in the graph,the instantaneous acceleration at time $t = 3\,s$ will be equal to $...........\,m/s^2$.