A motor boat going downstream overcomes a float at a point $A .60$ minutes later it turns and after some time passes the float at a distance of $12 \mathrm{km}$ from the point $A.$ The velocity of the stream is $n$ $\frac{\mathrm{km}}{\mathrm{h}}.$ The value of $n$ is (assuming constant velocity for the boat in still water)

A ball is projected vertically upwards at$t=0$. The ball is at same height at time $4 \mathrm{s}$ and $8 \mathrm{s}$. The maximum height attained by the ball is 

$\left(g=10 \mathrm{m} {{\mathrm{s}}^{-}}^2\right)$

The velocity-position graph of a particle moving in a straight line along$x$-axis is given below. Acceleration of particle at$x=2 \mathrm{m}$ is

The acceleration-position graph of a particle moving in a straight line along $x$-axis is shown in figure. The particle starts from rest at origin. The maximum speed of particle is

The acceleration-time graph of a particle moving in a straight line along $x$-axis is given below. If initial velocity of the particle is $4 \mathrm{m} {\mathrm{s}}^{-1}$, then velocity at $t=2 \mathrm{s}$ is