$A$ gun fires a small bullet with kinetic energy $K$. Then the kinetic energy of the gun while recoiling is

Two blocks $A$ and $B$ of masses $1\, kg$ and $2\, kg$ are connected together by a spring and are resting on a horizontal surface. The blocks are pulled apart so as to stretch the spring and then released. The ratio of $K.E.$ of block $A$ to the $K.E.$ of block $B$ is:

$A$ bomb of mass $9 \ kg$ explodes into two pieces of masses $3 \ kg$ and $6 \ kg$. The velocity of mass $3 \ kg$ is $16 \ m/s$. The $KE$ of mass $6 \ kg$ is ............ $J$.

$A$ bullet of mass $m$ is fired from a gun of mass $M$. If the velocity of the bullet is $v$,what will be the recoil velocity of the gun?

$A$ body of mass $5 \ kg$ initially at rest explodes into three fragments. The ratio of the masses of the three fragments is $1 : 1 : 3$. The two fragments of equal mass move in mutually perpendicular directions with a velocity of $21 \ m/s$. What is the velocity of the heaviest fragment in $m/s$?

$A$ ball of mass $200\,g$ rests on a vertical post of height $20\,m$. $A$ bullet of mass $10\,g$,travelling in a horizontal direction,hits the centre of the ball. After the collision,both travel independently. The ball hits the ground at a distance of $30\,m$ and the bullet at a distance of $120\,m$ from the foot of the post. The value of the initial velocity of the bullet will be $............m/s$ (if $g = 10\,m/s^2$).