Gravitational forces operate among which of the following?

Velocities $(v)$ and accelerations (a) in two systems of units 1 and 2 are related as $v_2=\frac{n}{m^2} v_1$ and $a_2=\frac{a_1}{m n}$ respectively. Here $m$ and $n$ are constants. Dimensionally relations between distances ( $s_1$ and $s_2$ ) and times ( $t_1$ and $t_2$ ) in the two systems are respectively

A body starts rest with uniform acceleration. If its velocity after $n^{\text {th }}$ second (last second) is $v$ then its displacement in the last two seconds is

A stone projected from the ground with a velocity $50 \mathrm{~ms}^{-1}$ at an angle of $30^{\circ}$ with the horizontal crosses a wall after a time of 3 s . Then the horizontal distance beyond the wall that the stone strikes the ground is (acceleration due to gravity $=10 \mathrm{~ms}^{-2}$ )