Two blocks of masses 2 kg and 1 kg respectively, are tied to the ends of a string which passes over a light frictionless pulley as shown in the figure below. The masses are held at rest at the same horizontal level and then released. The distance traversed by the centre of mass in 2 s is _______ m. (Take $g = 10 \; m/s^2$)

A particle having charge $10^{-9}$ C moving in $x$-$y$ plane in fields of $0.4 \hat{j}$ N/C and $4 \times 10^{-3} \hat{k}$ T experiences a force of $(4 \hat{i} + 2 \hat{j}) \times 10^{-10}$ N. The velocity of the particle at that instant is _________ m/s.

If X and Y are the inputs, the given circuit works as _________.

If a body of mass 1 kg falls on the earth from infinity, it attains velocity (v) and kinetic energy (k) on reaching the surface of earth. The values of v and k respectively are __________.

(Take radius of earth to be 6400 km and g = 9.8 m/s²)