When two balls at the same temperature collide,which of the following quantities is conserved?

$A$ bullet is fired from a rifle,and the rifle experiences recoil. What will be the kinetic energy of the recoiling rifle?

$A$ shell,in flight,explodes into four unequal parts. Which of the following is conserved?

$A$ block of mass $10 \ kg$ moving with a velocity of $5 \hat{i} \ m \ s^{-1}$ on a frictionless horizontal surface suddenly explodes into two pieces. If one piece with mass $4 \ kg$ moves with a velocity of $10 \hat{i} \ m \ s^{-1}$,then the velocity of the second piece is:

$A$ body of mass $1 \,kg$, initially at rest, explodes and breaks into three parts. The masses of the parts are in the ratio $1: 1: 3$. The two pieces of equal mass fly off perpendicular to each other with a speed of $30 \,m/s$ each. The velocity of the heavier part in $m/s$ is

$A$ body of mass $50 \, kg$ is projected vertically upwards with a velocity of $100 \, m/s$. After $5 \, s$,the body breaks into two pieces of mass $20 \, kg$ and $30 \, kg$. If the $20 \, kg$ piece travels upwards with a velocity of $150 \, m/s$,what is the velocity of the $30 \, kg$ block?